Target Tracking for image-guided radiation treatment

ABSTRACT

Systems, methods, and related computer program products for medical imaging and image-guided radiation treatment (IGRT) are described. In one preferred embodiment, an IGRT system provides intrafraction target tracking based on a comparison of intrafraction x-ray tomosynthesis image data with initial x-ray tomosynthesis image data acquired with the patient in an initial treatment position, the initial x-ray tomosynthesis image data having an inherent registration with co-acquired image data from a setup imaging system integral with, or having known geometry relative to, the tomosynthesis imaging system. Repeated registration of intrafraction x-ray tomosynthesis image data with pre-acquired reference image data from a different frame of reference is not required during intrafraction radiation delivery. Advantages include streamlined intrafraction computation and/or reduced treatment delivery margins.

PRIORITY CLAIM

This application claims priority to U.S. provisional application No.61/352,637 filed Jun. 8, 2010 and U.S. provisional application No.61/371,733 filed on Aug. 8, 2010.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of the instant patent application is related to thesubject matter of the commonly assigned U.S. Application No. 13/033,584filed on Feb. 23, 2011, which is incorporated by reference herein.

FIELD

This provisional patent specification relates to medical imaging andimage guided radiation treatment. More particularly, this provisionalpatent specification relates to systems, methods, and related computerprogram products for x-ray based medical imaging and x-ray basedimage-guided radiation treatment.

BACKGROUND

Pathological anatomies such as tumors and lesions can be treated with aninvasive procedure, such as surgery, which can be harmful and full ofrisks for the patient. A non-invasive method to treat a pathologicalanatomy (e.g., tumor, lesion, vascular malformation, nerve disorder,etc.) is external beam radiation therapy, which typically uses atherapeutic radiation source, such as a linear accelerator (LINAC), togenerate radiation beams, such as x-rays. In one type of external beamradiation therapy, a therapeutic radiation source directs a sequence ofx-ray beams at a tumor site from multiple co-planar angles, with thepatient positioned so the tumor is at the center of rotation (isocenter)of the beam. As the angle of the therapeutic radiation source changes,every beam passes through the tumor site, but passes through a differentarea of healthy tissue on its way to and from the tumor. As a result,the cumulative radiation dose at the tumor is high and that to healthytissue is relatively low.

The term “radiosurgery” refers to a procedure in which radiation isapplied to a target region at doses sufficient to necrotize a pathologyin fewer treatment sessions or fractions than with delivery of lowerdoses per fraction in a larger number of fractions. Radiosurgery istypically characterized, as distinguished from radiotherapy, byrelatively high radiation doses per fraction (e.g., 500-2000 centiGray),extended treatment times per fraction (e.g., 30-60 minutes pertreatment), and hypo-fractionation (e.g., one to five fractions ortreatment days). Radiotherapy is typically characterized by a low doseper fraction (e.g., 100-200 centiGray), shorter fraction times (e.g., 10to 30 minutes per treatment) and hyper-fractionation (e.g., 30 to 45fractions). For convenience, the term “radiation treatment” is usedherein to mean radiosurgery and/or radiotherapy unless otherwise noted.

Associated with each radiation therapy system is an imaging system toprovide in-treatment images that are used to set up and, in someexamples, guide the radiation delivery procedure and track in-treatmenttarget motion. Portal imaging systems place a detector opposite thetherapeutic source itself to image the patient for setup andin-treatment images, while other approaches utilize distinct,independent image radiation source(s) and detector(s) for the patientset-up and in-treatment images. Target or target volume tracking duringtreatment is accomplished by comparing in-treatment images topre-treatment image information. Pre-treatment image information maycomprise, for example, computed tomography (CT) data, cone-beam CT(CBCT) data, magnetic resonance imaging (MRI) data, positron emissiontomography (PET) data or 3D rotational angiography (3DRA) data, and anyinformation obtained from these imaging modalities (for example andwithout limitation digitally reconstructed radiographs or DRRs).

In one common scenario, the therapeutic source is a linear accelerator(LINAC) producing therapeutic radiation (which can be termed an “MVsource”) and the imaging system comprises one or more independent x-rayimaging sources producing relatively low intensity lower energy imagingradiation (each of which can be termed a “kV source”). In-treatmentimages can comprise one or more (preferably two) two-dimensional images(typically x-ray) acquired at one or more different points of view(e.g., stereoscopic x-ray images), and are compared with two-dimensionalDRRs derived from the three dimensional pre-treatment image information.A DRR is a synthetic x-ray image generated by casting rays through the3D imaging data, where the rays simulate the geometry of thein-treatment x-ray imaging system. The resulting DRR then hasapproximately the same scale and point of view as the in-treatment x-rayimaging system, and can be compared with the in-treatment x-ray imagesto determine the position and orientation of the target, which is thenused to guide delivery of radiation to the target.

X-ray tomosynthesis refers to the process of acquiring a number oftwo-dimensional x-ray projection images of a target volume using x-raysthat are incident upon the target volume at a respective number ofdifferent angles, followed by the mathematical processing of thetwo-dimensional x-ray projection images to yield a set of one or moretomosynthesis reconstructed images representative of one or morerespective slices of the target volume, wherein the number of x-rayprojection images is less than that in a set that would be required forCT image reconstruction, and/or the number or range of incidentradiation angles is less than would be used in a CT imaging procedure.Commonly, a plurality of tomosynthesis reconstructed images aregenerated, each being representative of a different slice of the targetvolume, and therefore a set of tomosynthesis reconstructed images issometimes referred to as a tomosynthesis volume. As used herein, theterm tomosynthesis projection image refers to one of the two-dimensionalx-ray projection images acquired during the tomosynthesis imagingprocess.

For purposes of the above terminology, for some preferred embodiments, aset of images that is required for CT image reconstruction is consideredto include images (e.g., 300 or more) generated over a range of incidentangles that is 180 degrees plus the fan beam angle. For some preferredembodiments, the x-ray projection images for constructing atomosynthesis image are taken over an angular range between 1 degree andan angular range value that is less than that needed for a completeprojection set for CT imaging (e.g., 180 degrees plus the fan angle),wherein the number of projection images generated in this range is avalue that is between 2 and 1000. In other preferred embodiments, thex-ray projection images for constructing a tomosynthesis image are takenover an angular range of between 5 degrees and 45 degrees, wherein thenumber of projection images generated in this range is between 5 and100.

X-ray tomosynthesis has been proposed as an in-treatment kV imagingmodality for use in conjunction with radiation treatment systems. InU.S. Pat. No. 7,532,705B2 it is proposed to process thethree-dimensional pre-treatment image information (e.g., a planning CTimage volume) to generate digital tomosynthesis (DTS) reference imagedata of a target located within or on a patient, such as by simulatingx-ray cone-beam projections through the planning CT image volume.Subsequently, with the patient on the treatment bed, DTS verificationimages are generated by acquiring a number of x-ray cone beam images atdifferent angles. Target localization is then performed by comparinglandmarks, such as bony structures, soft-tissue anatomy, implantedtargets, and skin contours in the DTS reference image data and DTSverification image data. In U.S. Pat. No. 7,711,087B2 it is proposed toacquire tomosynthesis image data during a treatment session. Forpurposes of movement tracking during the treatment session,tomosynthesis reconstructed slices are processed directly in conjunctionwith reference CT data in a process that searches for a tomosynthesisreconstructed image that best matches a selected reference CT slice. Theidentity of the particular tomosynthesis reconstructed image that yieldsa maximum degree of match, together with the amount of spatial offsetrequired for that tomosynthesis reconstructed image to achieve the peakmatch, is used to localize the target in three-dimensional space.

Cone beam CT (CBCT) has also been proposed as an in-treatment imagingmodality for use in conjunction with radiation treatment systems, insome cases as a kV imaging modality and in other cases as an MV (portal)imaging modality. Whereas conventional CT imaging reconstructs 2D slicesfrom 1D projections through a target volume, the 2D slices then beingstacked to form a 3D volumetric image, CBCT imaging directly constructsa 3D volumetric image from 2D projections of the target volume. As knownin the art, CBCT offers the ability to form a 3D image volume from asingle gantry rotation about the target volume, whereas conventional CTrequires one rotation per slice (for single-row detectors) or 1/Mrotations per slice (for newer quasi-linear multi-row detectors having Mrows). CBCT also provides for a more isotropic spatial resolution,whereas conventional CT limits the spatial resolution in thelongitudinal direction to the slice thickness. However, becauseconventional CT systems usually offer a substantially higher degree ofcollimation near their linear or quasi-linear row detectors than canusually be afforded by CBCT systems near their two-dimensionaldetectors, scattering noise and artifacts are more of a problem for CBCTsystems than for conventional CT systems.

In U.S. Pat. No. 7,471,765B2 it is proposed to use a CBCT imaging systemincluding a kV x-ray tube and a flat-panel imaging detector mounted on aLINAC gantry such that the kV radiation is approximately orthogonal tothe MV treatment radiation from the LINAC. Prior to treatment, a CBCTplanning image is acquired for treatment planning. Subsequently, beforeeach treatment fraction, a CBCT image is acquired and compared to theCBCT pre-treatment planning image, and the results of the comparison areused to modify the treatment plan for that treatment fraction tocompensate for interfraction setup errors and/or interfraction organmotion. Due to limitations in permissible gantry rotation speeds (e.g.,one rotation per minute) which cause the CBCT acquisition time to beslow compared to breathing (or other physiological cycles) of thepatent, a gating scheme synchronized to patient breathing (or otherphysiological cycles) is used during CBCT acquisition to reduce thedeleterious effects of organ motion in the reconstructed images. Alsodue to the relatively slow CBCT acquisition time, the CBCT volume datais generally useful only for patient set-up before each treatmentfraction, and not for intra-fraction motion correction.

X-ray source arrays such as field emission “cold cathode” x-ray sourcearrays represent a promising advance in medical imaging and offerpotential advantages over conventional x-ray tube sources in severalrespects. A conventional x-ray tube usually comprises a tungsten,tantalum or rhenium cathode that is heated to approximately 2000° C. tocause electrons to be emitted thermionically, the free electrons thenbeing accelerated toward an anode by a high electrical potential such as120 kV. X-ray radiation usable for imaging is created when thethermionically generated electrons strike an anode, usually made oftungsten, molybdenum, or copper, at a focal spot of the x-ray tube, thecollision causing the emission of x-ray photons. While historicallybeing the only practical and cost-effective way to provide imaging x-rayradiation in medical imaging environments, conventional x-ray tubesources can bring about many design compromises in view of theirrelatively large size and weight, high operating temperatures, highpower consumption, relatively modest temporal resolution (e.g., on/offswitching times), and their minimal amenability to miniaturization orformation into closely spaced arrays.

As an alternative to conventional x-ray tube technology in which freeelectrons are generated by thermionic emission, alternative technologieshave been introduced in which the free electrons are generated by fieldemission. In a field emission source, free electrons are emitted uponthe application of a voltage to a material having a high emissiondensity, such as certain carbon nanotube (CNT) materials. Because fieldemission of electrons is produced by a high electric field, no heatingis necessary. Field emission sources are thus often referred to as coldcathode sources. Advantageously, the electron beams emitted by suchmaterials may have low divergence and thus provide ease of focusing ontoa focal spot. Moreover, the virtually instantaneous response of thesource offers time gating capabilities that may even be on the order ofnanoseconds. Because they can be made exceedingly small, field emissionx-ray sources are highly amenable to formation into arrays. According toU.S. Pat. No. 7,505,562B2, which is incorporated by reference herein,devices having 1000 pixels per meter (i.e., 1000 individual x-raysources per meter) with pulse repetition rates on the order of 10 MHzcan be envisioned using technology within the current state of the art.

As used herein, the term x-ray source array refers to a source of x-rayscomprising a plurality of spatially distinct, electronically activatiblex-ray emitters or emission spots (focal spots) that are addressable onat least one of an individual and groupwise basis. Although most x-raysource arrays suitable for use with one or more of the preferredembodiments will commonly be of the field emission “cold cathode” type,the scope of the present teachings is not so limited. By way of example,other types of x-ray source arrays that may be suitable for use with oneor more of the preferred embodiments include scanning-beam array X-raysources in which an electron beam digitally scans across a tungstentransmission target thirty times per second, sequentially producing tenthousand individually collimated X-ray beams, as reported by Triple RingTechnologies, Inc., of Newark, Calif.

X-ray source arrays have been proposed for use in kV imaging systemsassociated with radiation treatment systems, such as in US20090296886A1.However, it is believed that substantial advances in the configuration,operation, and/or manner of integration of x-ray source arrays into IGRTsystems, such as those provided by one or more of the preferredembodiments herein, are needed in order to achieve clinicalpracticality, effectiveness, and market acceptance. It is to beappreciated the although particularly advantageous in the context ofIGRT systems, one or more of the preferred embodiments is alsoapplicable to a wide variety of other medical imaging applicationsoutside the realm of image-guided radiation treatment.

More generally, one or more issues arises with respect to known medicalimaging and/or radiation treatment systems that is at least partiallyaddressed by one or more of the preferred embodiments described furtherhereinbelow. Other issues arise as would be apparent to a person skilledin the art in view of the present teachings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a radiation treatment environment 100 within whichone or more of the preferred embodiments is advantageously applied.

FIG. 2 illustrates an IGRT system 200 having tomosynthesis imagingcapability according to a preferred embodiment.

FIG. 3 illustrates an IGRT system 300 having tomosynthesis imagingcapability according to a preferred embodiment.

FIG. 4 illustrates an IGRT system 400 having a stereoscopictomosynthesis imaging capability according to a preferred embodiment.

FIG. 5 illustrates an IGRT system 500 having a stereoscopictomosynthesis imaging capability according to a preferred embodiment.

FIG. 6 illustrates a simplified cross-sectional view of an IGRT system600 having a tomosynthesis imaging capability according to a preferredembodiment, the IGRT system 600 being implemented in the form of arotating gantry structure.

FIG. 7 illustrates image guided radiation treatment (IGRT) of a bodypart by an IGRT apparatus according to a preferred embodiment.

FIG. 8A illustrates image guided radiation treatment of a body part byan IGRT apparatus according to another preferred embodiment.

FIG. 8B illustrates a layout of simplified conceptual versions of thevarious images involved in the method of FIG. 8A.

FIG. 8C illustrates the simplified conceptual image versions of FIG. 8Btogether with simplified graphical representations of transformations“T” associated with selected registrations therebetween to be performedaccording to one or more of the preferred embodiments.

FIGS. 9A-9C illustrate image guided radiation treatment of a body partby an IGRT apparatus according to another preferred embodiment that issimilar in certain respects to the preferred embodiment of FIG. 8A,except that the tomosynthesis imaging system of the IGRT apparatus isalso used as the setup imaging system.

FIG. 10 illustrates a tomosynthesis imaging system 1000 as may beintegrated into one or more of the above-described IGRT systemsaccording to a preferred embodiment, the tomosynthesis imaging system1000 providing dual-energy stereoscopic tomosynthesis imaging accordingto a preferred embodiment.

FIG. 11A illustrates selective collimation of x-ray emission from anx-ray source array according to a preferred embodiment.

FIG. 11B illustrates selective collimation of x-ray emission from anx-ray source array according to another preferred embodiment.

FIGS. 11C-11D conceptually illustrate two-dimensional imaging andtracking of a target according to a preferred embodiment using, by wayof example, the two-dimensional x-ray imaging apparatus of FIG. 11B.

FIG. 12A illustrates an x-ray source collimation device COLL and anx-ray source array SA according to a preferred embodiment.

FIG. 12B illustrates an x-ray source collimation device COLL and anx-ray source array SA according to a preferred embodiment in which thex-ray beams are dynamically steered according to actuation of thedirection of the louvers L.

FIG. 13 illustrates a simplified perspective view of an x-ray sourcecollimation device COLL and an x-ray source array SA according to apreferred embodiment, the collimation device COLL comprising a firststeerable louver array LX and a second steerable louver array LY.

FIG. 14 illustrates a smaller scale (i.e., less detailed) conceptualside view of an x-ray source array SA and collimator COLL according to apreferred embodiment.

FIGS. 15-16 each illustrate reduced dosage x-ray imaging (or higherquality imaging for a predefined x-ray dose) and target tracking of atarget structure T using an x-ray source array SA and an x-raycollimating device COLL according to a preferred embodiment.

FIG. 17-1 through FIG. 17-5 illustrate acquiring a set of x-raytomosynthesis projection images of a target volume according to apreferred embodiment.

FIG. 18 illustrates acquiring a set of x-ray tomosynthesis projectionimages of a target volume according to a preferred embodiment in which(i) the digital detector units DDU1-DDU5 are non-overlapping with eachother, and (ii) the x-ray source array units SAU and x-ray collimatingunits XCU are configured such that each separate x-ray source array unitilluminates only its paired digital detector unit DDU with primaryx-rays, with no spillover of primary x-rays onto neighboring digitaldetector units.

FIG. 19-1 through FIG. 19-5 illustrate acquiring a set of x-raytomosynthesis projection images of a target structure T according to apreferred embodiment.

FIG. 20 illustrates acquiring a set of x-ray tomosynthesis projectionimages of a target volume according to a preferred embodiment similar tothat of FIG. 19-1 through FIG. 19-5, except that all of the x-raytomosynthesis projection images are acquired simultaneously.

FIG. 21-1 through FIG. 21-5 illustrates acquiring a set of x-raytomosynthesis projection images of a target volume according to apreferred embodiment.

FIG. 22 illustrates acquiring a set of x-ray tomosynthesis projectionimages of a target volume according to a preferred embodiment similar tothat of FIG. 21-1 through FIG. 21-5, except that all of the x-raytomosynthesis projection images are acquired simultaneously.

FIGS. 23A-23D illustrate an inverse geometry tomosynthesis imagingsystem 2301 that can be used in tomosynthesis imaging according to apreferred embodiment.

FIG. 24 illustrates inverse geometry tomosynthesis imaging of a targetstructure located within a target volume according to a preferredembodiment.

DESCRIPTION

FIG. 1 illustrates a radiation treatment environment 100 within whichone or more of the preferred embodiments is advantageously applied. Theradiation treatment environment 100 includes a reference imaging system102 and an IGRT system 104. Reference imaging system 102 usuallycomprises a high precision volumetric imaging system such as a computedtomography (CT) system or a nuclear magnetic resonance imaging (MRI)system. In view of cost and workflow considerations in many clinicalenvironments, the reference imaging system 102 is often a generalpurpose tool used for a variety of different purposes in the clinic orhospital environment, and is not specifically dedicated to the IGRTsystem 104. Rather, the reference imaging system 102 is often located inits own separate room or vault and is purchased, installed, and/ormaintained on a separate and more generalized basis than the IGRT system104. Accordingly, for the example of FIG. 1, the reference imagingsystem 102 is illustrated as being distinct from the IGRT system 104.Notably, for other radiation treatment environments that are not outsidethe scope of the present teachings, the reference imaging system 102 canbe considered as an integral component of the IGRT system 104.

IGRT system 104 comprises a radiation treatment (MV) source 108 thatselectively applies high-energy x-ray treatment radiation to a targetvolume of a patient P positioned on a treatment couch C. The MV source108 applies the treatment radiation under the control of a systemcontroller 114, and more particularly a treatment radiation controlsubsystem 128 thereof. System controller 114 further comprisesprocessing circuitry 120, a detector controller 122, a couch positioncontroller 124, and a kV radiation controller 126 each programmed andconfigured to achieve one or more of the functionalities describedfurther herein. One or more imaging (kV) radiation sources 110selectively emit relatively low-energy x-ray imaging radiation under thecontrol of kV radiation controller 126, the imaging radiation beingcaptured by one or more imaging detectors 112. In alternative preferredembodiments, one or more of the imaging detectors 112 can be a so-calledportal imaging detector that captures high-energy x-ray treatmentradiation from MV source 108 that has propagated through the targetvolume.

For one preferred embodiment, the kV imaging radiation sources 110include both a two-dimensional stereotactic x-ray imaging system and atomosynthesis imaging system. For other preferred embodiments, only atwo-dimensional stereotactic x-ray imaging system is provided, while forstill other preferred embodiments only a tomosynthesis imaging system isprovided. Preferably, each of the stereotactic x-ray imaging system andthe tomosynthesis imaging system are characterized by either (a) afixed, predetermined, nonmoving geometry relative to the (x, y, z)coordinate system of the treatment room, or (b) a precisely measurableand/or precisely determinable geometry relative to the (x, y, z)coordinate system of the treatment room in the event they aredynamically moveable. The MV radiation source 108 should also, ofcourse, have a precisely measurable and/or precisely determinablegeometry relative to the (x, y, z) coordinate system of the treatmentroom.

A couch positioner 130 is actuated by the couch position controller 124to position the couch C. A non-x-ray based position sensing system 134senses position and/or movement of external marker(s) strategicallyaffixed to the patient, and/or senses position and/or movement of thepatient skin surface itself, using one or more methods that do notinvolve ionizing radiation, such as optically based or ultrasonicallybased methods. In one example, IGRT system 104 can be similar to aCYBERKNIFE® robotic radiosurgery system available from AccurayIncorporated of Sunnyvale, Calif., and the non-x-ray position sensingsystem 134 can be similar to relevant sensing components of the AccurayIncorporated SYNCHRONY® respiratory tracking system. IGRT system 104further includes an operator workstation 116 and a treatment planningsystem 118.

In common clinical practice, treatment planning is performed on apre-acquired treatment planning image 106 generated by the referenceimaging system 102. The pre-acquired treatment planning image 106 isoften a high resolution three-dimensional CT image acquiredsubstantially in advance (e.g., one to two days in advance) of the oneor more radiation treatment fractions that the patient will undergo. Asindicated in FIG. 1 by the illustration of an (i, j, k) coordinatesystem for the treatment planning image 106, which is in contrast to the(x, y, z) treatment room coordinate system illustrated for the treatmentroom of the IGRT system 104, there is generally no pre-existing orintrinsic alignment or registration between the treatment planning image106 coordinate system and the treatment room coordinate system. Duringthe treatment planning process, a physician establishes a coordinatesystem (e.g., i, j, k in treatment planning image 106) within thetreatment planning image, which may also be referred to herein as theplanning image coordinate system or planning image reference frame. Aradiation treatment plan is developed in the planning image coordinatesystem that dictates the various orientations, sizes, durations, etc.,of the high-energy treatment radiation beams to be applied by the MVsource 108 during each treatment fraction. Accurate delivery oftherapeutic radiation to a target requires aligning the planning imagecoordinate system with the treatment room coordinate system as theentire delivery and tracking system (if present) is calibrated to thetreatment room coordinate system. It will be appreciated that thisalignment does not need to be exact and further appreciated that couchadjustment or beam delivery adjustment can be used to account foroffsets in the alignment between the two coordinate systems.

Thus, immediately prior to each treatment fraction, under a preciseimage guidance of the kV imaging radiation sources 110 according to oneor more of the embodiments described further hereinbelow, the patient isphysically positioned such that the planning image coordinate system(defined, for example and not by way of limitation, by a physician whilecreating a treatment plan on a CT image or planning image) is positionedinto an initial alignment with the treatment room coordinate system,hereinafter termed an initial treatment alignment or initial treatmentposition. This alignment is commonly referred to as patient set up.Depending on the location of the target volume, the target volume canvary in position and orientation and/or can undergo volumetricdeformations due to patient movement and/or physiological cycles such asrespiration. As used herein, the term in-treatment alignment variationor in-treatment position variation is used to refer to the variations inposition, orientation, and/or volumetric shape by which the currentstate of the target volume differs from the initial treatment alignment.By virtue of a known relationship between the treatment planningcoordinate system and the treatment room coordinate system, the termin-treatment alignment variation can also be used to refer to thevariations in position, orientation, or volumetric shape by which thecurrent state of the target volume differs from that in the treatmentplanning coordinate system. More generally, the term initial treatmentalignment or initial treatment position refers herein to the particularphysical pose or disposition (including position, orientation andvolumetric shape) of the body part of the patient upon patient setup atthe outset of the treatment fraction. The term intrafraction alignmentor intrafraction position refers herein to the particular physical poseor disposition (including position, orientation or volumetric shape) ofthe body part of the patient during the treatment fraction.

A non x-ray based position sensing system 134 may also be provided. Thisnon x-ray based position sensing system 134 may include, by way ofexample and without limitation, external markers affixed in some mannerto a patient's chest which move in response to respiration (othermechanisms for monitoring respiration may be used), and include a monoor stereoscopic x-ray imaging system, which as described above canprecisely determine target location. System 134 correlates motion of theexternal markers with target motion, as determined from (for example)the mono or stereoscopic x-ray projections. Non x-ray based positionsensing system 134, therefore, permits system controller 114 to monitorexternal marker motion, use the correlation model to precisely predictwhere the target will be located in real time (e.g., ˜60 Hz), and directthe treatment beam to the target. As treatment of the moving targetprogresses additional x-ray images may be obtained and used to verifyand update the correlation model.

According to a preferred embodiment, system controller 114 includingprocessing circuitry 120 is configured and programmed to receiveinformation from the non-x-ray based position sensing system 134 and theimaging detector(s) 112 or just from the imaging detector(s) 112 whentreating a relatively stationary target volume (for example and withoutlimitation a brain, spine or prostate tumor), compute an in-treatmentalignment variation therefrom, and control the treatment radiationsource 108 in a manner that compensates for the in-treatment alignmentvariation on a real-time basis. In the case where the target volumemoves due to respiration, the more information-rich x-ray-based datafrom the imaging detectors 112 is updated at a relatively slow ratecompared to the breathing cycle of the patient (for example, once every15 seconds) to maintain reasonably low x-ray imaging dose levels, theless information-rich data from the non-x-ray based position sensingsystem 134 can be updated in substantially real-time (for example, 30times per second). Using methods such as those described in the commonlyassigned U.S. Pat. No. 6,501,981B1, a correlation model between one ormore x-ray-sensed internal target volume (with or without fiducials) andone or more non-x-ray-sensed external markers is used to ascertain thein-treatment alignment variations on a real-time basis, the correlationmodel being updated (corrected) at each x-ray imaging interval.Advantageously, judicious x-ray/tomosynthesis imaging source collimationstrategies according to one or more of the preferred embodimentsdescribed further infra can be advantageously used to improvedetermination of in-treatment alignment variations or target tracking byvirtue of one or more of higher x-ray/tomosynthesis imaging quality,reduced x-ray radiation dose, and higher x-ray/tomosynthesis imagingdata acquisition rates.

It is to be appreciated that the use of a non-x-ray based positionsensing system 134 such as the SYNCHRONY® respiratory tracking systemrepresents an option that, while advantageous in the radiation treatmentof certain tumors within the lung or chest area, is not required forradiation treatments in many other body parts, such as the prostate,spine or brain. Whereas x-ray dosage concerns provide limits on thenumber of kV x-ray images that should be acquired in any particularintrafraction time interval (for example, no more than one kV imageevery 15 seconds, every 30 seconds, or every 60 seconds), tumors withinthe chest area can move at substantially faster periodic rates,therefore giving rise to the need for the non-x-ray based positionsensing system 134. However, tumors in other parts of the body, such asthe prostate, will generally experience motion on a much slower timescale, wherein the dose-limited kV x-ray imaging rate will be still besufficiently high to effectively guide the radiation treatment. Theprostate, for example, may experience movement due to an accumulation ofurine in the nearby urinary bladder, an event for which one kV x-rayimage every 60 seconds should be sufficient to track resultant movement.Accordingly, for the many other parts of the anatomy for which kVimaging rates are sufficient, the non-x-ray based position sensingsystem 134 and the associated “real time” tracking (i.e., tracking at arate faster than the kV imaging rate) is not required.

It is to be appreciated that the exemplary radiation treatmentenvironment of FIG. 1 is presented by way of example and not by way oflimitation, that the preferred embodiments are applicable in a varietyof other radiation treatment environment configurations, and that one ormore of the preferred embodiments is applicable to general medicalimaging environments outside the particular context of radiationtreatment systems. Thus, for example, while one or more of the preferredembodiments is particularly advantageous when applied in the context ofa radiation treatment environment in which the reference imaging system102 is physically separated from, has no common coordinate system with,and/or has no other intrinsic means of volumetric image registrationwith the IGRT delivery system 104, the scope of the present teachings isnot so limited. Rather, the one or more preferred embodiments can alsobe advantageously applied in the context of radiation treatmentenvironments in which the reference imaging system is physicallyintegral with radiation treatment delivery system or has other intrinsiclinkages, such as a rail-based patient movement system, with theradiation treatment delivery system.

As used herein, “registration” of medical images refers to thedetermination of a mathematical relationship between correspondinganatomical or other (e.g. fiducials) features appearing in those medicalimages. Registration can include, but is not limited to, thedetermination of one or more spatial or alignment or intrafractiontransformations that, when applied to one or both of the medical images,would cause an overlay of the corresponding anatomical features. Thespatial or alignment or intrafraction transformations can includerigid-body transformations and/or deformable transformations and can, ifthe medical images are from different coordinate systems or referenceframes, account for differences in those coordinate systems or referenceframes. For cases in which the medical images are not acquired using thesame imaging system and are not acquired at the same time, theregistration process can include, but is not limited to, thedetermination of a first transformation that accounts for differencesbetween the imaging modalities, imaging geometries, and/or frames ofreference of the different imaging systems, together with thedetermination of a second transformation that accounts for underlyinganatomical differences in the body part that may have taken place (e.g.,positioning differences, overall movement, relative movement betweendifferent structures within the body part, overall deformations,localized deformations within the body part, and so forth) betweenacquisition times. The term alignment transformation refers herein to atransformation between a first coordinate system (for example and not byway of limitation a planning image coordinate system of a patient) and asecond coordinate system (a treatment room coordinate system) wherebythe alignment transformation determines the location of a target in thesecond coordinate system relative to the first coordinate system, forexample and not by way of limitation at the time of patient setup priorto commencement of the treatment fraction. The term intrafractiontransformation refers herein to a transformation between the firstcoordinate system and the second coordinate system whereby theintrafraction transformation determines the location of the target inthe first coordinate system relative to the second coordinate systemfollowing commencement of the procedure, for example and not by way oflimitation during the treatment fraction.

FIG. 2 illustrates an IGRT system 200 having tomosynthesis imagingcapability according to a preferred embodiment. IGRT system 200 includesan MV radiation source 204 mounted on an articulated robot arm 202, andfurther includes a kV x-ray imaging system comprising dual conventionalkV sources 206 and 208 translatably mounted on a ceiling-supportedsupport rail 210 extending in an arc over and opposite a floor-mountedkV imaging detector 204. In a first mode of operation, the x-ray sources206 and 208 can remain fixed at opposite ends of the rail 210 and, inconjunction with corresponding opposing ends of the kV imaging detector204, can function as a stationary two-dimensional stereoscopic x-rayimaging system. In the first mode of operation, the patient alignmentprocess (and, optionally, the in-treatment target tracking process) canproceed based on comparisons of stereoscopic x-ray images and digitallyreconstructed radiographs (DRR's) derived from a reference volume asdescribed, for example, in the commonly assigned U.S. Pat. No.7,204,640B2, U.S. Pat. No. 7,684,647B2, US 20050049478A1, andUS20080130825A1, a process that has been continuously improved over theyears and has proven highly robust and effective. Similar methods havebeen used with substantial clinical and commercial success, such as inthe CYBERKNIFE® system from Accuray Incorporated, which tracks, detectsand corrects for tumor and patient movement during treatment andprecisely delivers high doses of radiation to a tumor typically withsub-millimeter accuracy. In a second mode of operation, the kV source206 and/or the kV source 208 can be dynamically translated in atomosynthesis imaging arc along the rail 210 to achieve tomosynthesisimaging in conjunction with the full spatial extent of the imagingdetector 204.

Included in FIG. 2 is a schematic diagram of a computer system 250integrated with and/or coupled to the IGRT system 200 using one or morebusses, networks, or other communications systems 260, including wiredand/or wireless communications systems, and being capable in conjunctiontherewith of implementing the methods of one or more of the preferredembodiments. Methods of image guided radiation treatment in accordancewith one or more of the preferred embodiments may be implemented inmachine readable code (i.e., software or computer program product) andperformed on computer systems such as, but not limited to, the computersystem 250, wherein a central processing unit (CPU) 251 including amicroprocessor 252, random access memory 253, and nonvolatile memory 254(e.g. electromechanical hard drive, solid state drive) is operated inconjunction with various input/output devices, such as a display monitor255, a mouse 261, a keyboard 263, and other I/O devices 256 capable ofreading and writing data and instructions from machine readable media258 such as tape, compact disk (CD), digital versatile disk (DVD),blu-ray disk (BD), and so forth. In addition, there may be connectionsvia the one or more busses, networks, or other communications systems260 to other computers and devices, such as may exist on a network ofsuch devices, e.g., the Internet 259. Software to control the imageguided radiation treatment steps described herein may be implemented asa program product and stored on a tangible storage device such as themachine readable medium 258, an external nonvolatile memory device 262,or other tangible storage medium. For clarity of presentation, thecomputer system 250 of FIG. 2 is omitted from further drawings and/ordescriptions hereinbelow. Methods for configuring and programming thecomputer system 250 for achieving the functionalities described hereinwould be apparent to a person skilled in the art in view of the presentdisclosure.

Referring again to FIG. 2, according to one alternative preferredembodiment, the kV imaging sources 206 and 208 are fixably located atopposite ends of the rail 210, and are augmented by a plurality ofdetector-facing x-ray source arrays (not shown) distributed across adetector-facing surface 212 of the rail 210. A stereoscopic x-rayimaging mode of operation can be carried out by the kV imaging sources206 and 208 kV in conjunction with opposing ends of the detector 204,while a tomosynthesis imaging mode of operation can be carried out bythe x-ray source arrays (without physically moving the x-ray sourcearrays) in conjunction with the full spatial extent of the imagingdetector 204. In another alternative preferred embodiment the kV imagingsources 206 and 208 are omitted altogether, wherein a stereoscopic x-rayimaging mode is achieved by operating only the particular x-ray arraysources and detectors disposed near opposing ends of the rail 212, andwherein a tomosynthesis imaging mode of operation is carried out usingthe full spatial extent of the x-ray source arrays and imaging detector204.

FIG. 3 illustrates an IGRT system 300 having tomosynthesis imagingcapability according to a preferred embodiment. IGRT system 300 includesan MV radiation source 304 mounted on an articulated robot arm 302. TheIGRT system 300 further includes a kV x-ray imaging system comprising aplurality of x-ray array sources 306 and a corresponding plurality ofarray detectors 308 arranged linearly along opposing surfaces of a C-arm310. The C-arm 310 is, in turn, mounted on a robot arm 312 that permitsa wide variety of different positions and orientations of the kV imagingsystem. By virtue of precise robotic control of the C-arm 310, theprecise locations and orientations of the sources 306 and detectors 308relative to the treatment room coordinate system is known. Uponplacement of C-arm 310 into a desired imaging position, tomosynthesisimaging can proceed by selective activation of respective ones ofsources 306 and detectors 308 over a tomosynthesis imaging arc.Optionally, the kV imaging system can also be operated in a stereoscopicx-ray imaging mode by operating only the particular x-ray array sourcesand detectors at opposing ends of the linear arrangements.

FIG. 4 illustrates an IGRT system 400 having a stereoscopictomosynthesis imaging capability according to a preferred embodiment.The IGRT system 400 includes an MV radiation source 404 mounted on anarticulated robot arm 402. IGRT system 400 further comprises a firstx-ray source array 406 paired with a first x-ray detector array 412 toestablish a first “channel” of a stereoscopic x-ray tomosynthesisimaging system, and a second x-ray source array 408 paired with a secondx-ray detector array 410 to establish a second “channel.” For onepreferred embodiment, each channel can be configured in an inversegeometry tomosynthesis imaging arrangement, as described further infrawith respect to FIGS. 23A-23D and FIG. 24. The x-ray source arrays 406and 408 can be mounted in or near the floor of the treatment vault,while the x-ray detector arrays 410 and 412 can be mounted in or nearthe ceiling of the treatment vault, although the scope of the preferredembodiments is not so limited.

FIG. 5 illustrates an IGRT system 500 having a stereoscopictomosynthesis imaging capability according to a preferred embodiment.The IGRT system 500 is similar to the IGRT system 400 of FIG. 4, andincludes numbered components 502-512 similar to the numbered components402-412 of FIG. 4, respectively, except that the kV source and detectorarrays are positioned to form a stereoscopic arc extending along thehead-to-toe direction of the treatment couch rather than theleft-to-right direction as in FIG. 4. In an alternative preferredembodiment (not shown), the kV imaging features of FIGS. 4 and 5 can becombined, such that there are four (4) x-ray source arrays in or nearthe floor and four (4) x-ray detector arrays in or near the ceiling,such that stereoscopic imaging arcs along either (or both) of thehead-to-toe and left-to-right directions can be provided. In stillanother alternative preferred embodiment (not shown), the x-ray sourcearrays 506 and 508 can be positioned on an in-floor mechanical platterthat is capable of in-floor rotation around a vertical axis passingthrough the isocenter (not shown), and the x-ray detector arrays 510 and512 can be positioned on an in-ceiling mechanical platter capable ofin-ceiling rotation around that same vertical axis, wherein themechanical platters can be rotated to provide an option between theleft-to-right stereoscopic arc configuration of FIG. 4 and thehead-to-toe stereoscopic arc configuration of FIG. 5. In yet anotheralternative preferred embodiment (not shown), the x-ray source arrays506 and 508 can be replaced by a single long x-ray source array thatextends across the area collectively covered by both of them in FIG. 5and further includes all of the area lying between them, and the x-raydetector arrays 510 and 512 can likewise be replaced by a single longx-ray detector array that extends across the area collectively coveredby both of them in FIG. 5 and further includes all of the area lyingbetween them.

FIG. 6 illustrates a simplified cross-sectional view of an IGRT system600 having a tomosynthesis imaging capability according to a preferredembodiment, the IGRT system 600 being implemented in the form of arotating gantry structure. The IGRT system 600 includes an MV source 604mounted on a gantry frame 602 in a manner that permits 360 degreerotation around the patient, and further includes a kV imaging systemcomprising a plurality of x-ray array sources 606 and a correspondingplurality of array detectors 608 arranged along opposing surfaces of asupport ring 612 that is rotatable around the patient independently ofthe MV source 604. Upon rotation of the support ring 612 into a desiredimaging position, tomosynthesis imaging can proceed by selectiveactivation of respective ones of sources 606 and detectors 608 over atomosynthesis imaging arc. Optionally, the kV imaging system can also beoperated in a stereoscopic x-ray imaging mode by operating only theparticular x-ray array sources and detectors at opposing ends of thelinear arrangements along the support ring 612.

It is to be appreciated that one or more of the preferred embodimentsdescribed further infra can be implemented in conjunction with a widevariety of different radiation treatment delivery mechanisms, includingrobotic arm-based systems, C-arm gantry based systems, ring gantry-basedsystems, and barrel gantry-based systems, and that the particularexamples of FIGS. 2-4 are presented only by way of example and not byway of limitation. Other non-limiting examples of IGRT systemconfigurations suitable for use with one or more of the preferredembodiments include systems discussed in U.S. Pat. No. 7,188,999B2, U.S.Pat. No. 7,227,925B1, and the commonly assigned U.S. ProvisionalApplication Ser. No. 61/307,847, each of which is incorporated byreference herein.

FIG. 7 illustrates image guided radiation treatment (IGRT) of a bodypart by an IGRT apparatus according to a preferred embodiment. The IGRTapparatus includes a two-dimensional stereotactic x-ray imaging systemand a tomosynthesis imaging system each having known geometries relativeto the treatment coordinate system of the IGRT apparatus. At step 702, areference CT volume of the body part is received. At step 704, aradiation treatment plan for an application of treatment radiation tothe body part by the IGRT apparatus is developed. During the treatmentplanning process, a planning image coordinate system is established. Atstep 706, a population of two-dimensional stereotactic digitallyreconstructed radiograph (DRR) images is generated, based on the knownimaging geometry of the treatment room two-dimensional mono orstereotactic imaging system.

At step 708, which is preferably carried out immediately prior to thebeginning of radiation treatment, the body part is positioned into afirst treatment alignment with the treatment coordinate system byacquiring two-dimensional stereotactic x-ray images, and comparing theacquired stereotactic x-ray images to the DRR images. For one preferredembodiment, this patient alignment process proceeds according to one ormore methods described in the commonly assigned U.S. Pat. No.7,204,640B2, U.S. Pat. No. 7,684,647B2, US 20050049478A1, andUS20080130825A1. Even though based on feedback provided bytwo-dimensional stereotactic imaging, which provides lesser informationthan three-dimensional imaging modalities, such methods have beencontinuously improved and perfected over the years (for example, inrelation to the CYBERKNIFE® robotic radiosurgery system available fromAccuray Incorporated) and have proven precise, robust, and reliable.

At step 710, with the body part still in the first treatment alignment,a first tomosynthesis data set of the body part is acquired. By virtueof the known imaging geometries of the two-dimensional stereotacticx-ray imaging system and the tomosynthesis imaging system relative tothe treatment room, and by virtue of the precise and reliable nature ofthe positioning process of step 708, there is provided an intrinsic,highly precise registration between first tomosynthesis data set and theplanning image data set. The precision of this intrinsic registration iseven further facilitated in an optional preferred embodiment in which asame x-ray image source is shared between the tomosynthesis imagingsystem and the two-dimensional stereotactic x-ray imaging system.Alternatively, the intrinsic registration can be obtained by acquiringthe set up images (mono or stereo 2D images or CBCT image) substantiallysimultaneously. By “substantially simultaneous” it is meant that theimages are acquired within a time frame during which the target volumedoes not appreciably move such that inherent or intrinsic registrationbetween the two images can be assumed. Inherent or intrinsicregistration means that the two images are sufficiently aligned to carryout target tracking and radiation delivery to within the tolerance ofthe treatment plan being delivered. For a standard fractionatedradiotherapy case, the tolerances will not be as high whereas forhypofractionated radiosurgery sub millimeter tolerances may benecessary. It will be appreciated that when using a CBCT image as a setup image, data necessary for the first tomosynthesis can be obtainedfrom the data used to generate the CBCT image. In this latter case, theset up image and the first tomosynthesis image are generated from thevery same data.

Subsequent to the patient alignment process and the acquisition of thefirst tomosynthesis data set, and usually after the beginning ofradiation treatment (step 712), a subsequent tomosynthesis data set ofthe body part is acquired at step 714 using the tomosynthesis imagingsystem. At step 716, the subsequent tomosynthesis image data set isprocessed in conjunction with the first tomosynthesis data set tocompute an in-treatment alignment variation of the body part relative toat least one of the first treatment alignment and/or the planningcoordinate system, that is to say the subsequent tomosynthesis image isused to track intrafraction target motion. Without limitation, thein-treatment alignment variation can be measured and characterized by arigid body transformation and/or a non-rigid transformation foraccommodating elastic deformations in the body part during the treatmentdelivery. The transformation is used to adjust the patient relative tothe treatment beam or vice versa in order to deliver the radiationaccording to plan. Further tomosynthesis imaging data sets are acquiredon an ongoing basis (for example, every 15 seconds) and compared to oneor more previous tomosynthesis imaging data sets and/or the firsttomosynthesis imaging data set to achieve effective tracking ofin-treatment alignment variations throughout the radiation treatmentfraction.

Advantageously, the method of FIG. 7 harnesses the three-dimensional andspeedy character of tomosynthesis imaging for the important purpose oftracking deformable movement of the body part during the treatmentfraction, while at the same time harnessing tried and true patientpositioning methods based on x-ray stereoscopic and DRR imagecomparisons. The method is believed to provide one or more advantagesover methods such as those of U.S. Pat. No. 7,532,705B2 and U.S. Pat.No. 7,711,087B2. For example, although it is indeed possible to computealignments between (i) tomosynthesis data from simulated x-rayprojections through the reference CT volume, and (ii) tomosynthesis datafrom live projections through the patient, as set forth in U.S. Pat. No.7,532,705B2, this can be a highly computationally intensive process, andcan be subject to errors from inevitable differences between the virtualtomosynthesis imaging geometry of the simulated x-ray projections andreal-world tomosynthesis imaging geometry of the IGRT system. Likewise,although it is indeed possible to compute alignments between (i) slicesfrom reference CT volume, and (ii) tomosynthesis data from liveprojections through the patient, as set forth in U.S. Pat. No.7,711,087B2, this would also be highly computationally intensive andhighly subject to cross-modality, cross-acquisition-system errors.Advantageously, the method of FIG. 7 does not depend on a need tosimulate the tomosynthesis imaging geometry of the IGRT system, and doesnot depend on the need to directly compare data volumes from twodistinct imaging systems. Instead, the in-treatment tracking method ofFIG. 7 is directed to a more realistic, apples-to-apples alignmentcomputation between two (or more) tomosynthesis data sets acquired usingthe same tomosynthesis acquisition system, while the patient positioningprocess, which does indeed depend on comparing image data from twodifferent systems, harnesses tried and true methods based on x-raystereoscopic and DRR image comparisons.

Notably, although certain additional preferred embodiments describedhereinbelow do involve comparison between (i) the reference CT volume orother reference imaging modality (or image data abstracted therefromsuch as digitally reconstructed tomographs (DRTs)) and (ii)tomosynthesis image data from an on-board tomosynthesis imaging system,and therefore the need to perform registrations of image data fromdifferent frames of reference and/or different imaging modalities isindeed implicated, these difficult registrations only need to beperformed at patient setup and not during intrafraction radiationdelivery. Because these difficult computations can be computed prior tothe instantiation of radiation delivery, rather than during theintrafraction radiation delivery, their computational complexity becomesless of a problem, and time can be taken to compute an optimal result.

FIG. 8A illustrates image guided radiation treatment of a body part byan IGRT apparatus according to another preferred embodiment. For thispreferred embodiment, the IGRT apparatus includes a treatment guidanceimaging system having a known geometry relative to the reference frameof the IGRT apparatus, which can alternatively be termed an on-boardimaging system. The treatment guidance imaging system comprises acombination of a tomosynthesis imaging system and an additional medicalimaging system, the tomosynthesis imaging system being primarilydirected to facilitating intrafraction imaging of the target volume fortarget tracking, the additional medical imaging system being directedprimarily to facilitating a patient setup process in which the patientis positioned into an initial treatment position relative to the IGRTapparatus prior to instantiation of radiation delivery. The additionalmedical imaging system can be termed a setup imaging system, although itis to be appreciated that the scope of its functionality can extendbeyond patient setup without departing from the scope of the preferredembodiments.

According to one preferred embodiment, the setup imaging system and thetomosynthesis imaging system that form the treatment guidance imagingsystem are either integrated into a common set of imaging hardware orhave precisely known geometries relative to each other and the frame ofreference of the IGRT apparatus. It is not required that these preciselyknown geometries be static or permanently fixed, but only that theirgeometrical relationships be precisely known at any relevant point intime. Although there are many different modalities and configurationsthat can serve as the setup imaging system, in one preferred embodimentthe setup imaging system can be a CBCT imaging system, such as may beprovided by one or more of the IGRT systems disclosed in the commonlyassigned Ser. No. 61/307,847, supra, supra, and/or the IGRT apparatus600 of FIG. 6, supra. Thus, for example, in the IGRT apparatus 600 ofFIG. 6, in addition to the on-board tomosynthesis imaging systemprovided by virtue of the array sources 606 and the array detectors 608,there can also be provided an on-board CBCT system usable for patientsetup by virtue of an additional mode of operation in which the supportring 612 is rotated by a full 360 degrees (or at least 180 degrees plusthe fan beam angle) around the patient while one or more of the arraysources 606 and array detectors 608 is operated at regular angularintervals. Importantly, such CBCT system has an intrinsic, inherent,precisely known spatial registration with the tomosynthesis imagingsystem because its imaging hardware is integral therewith. For anotherpreferred embodiment, the onboard setup imaging system can alternativelycomprise a 2D stereo x-ray imaging system using that same hardware. Forother preferred embodiments, the onboard setup imaging system can be anultrasound system or a system of some other imaging modality, providedonly that it can be physically implemented in conjunction with thetomosynthesis imaging system and that its physical positioning andimaging geometry is known or can be precisely measured relative to theframe of reference of the tomosynthesis imaging system, the overall IGRTapparatus, and the treatment vault.

Referring again to FIG. 8A, at step 852 a pre-acquired image data set ofthe body part is received, the pre-acquired image data set having beenacquired in a reference frame generally independent of the referenceframe of the IGRT apparatus. In one preferred embodiment, thepre-acquired image data set may have been acquired using the referenceCT imaging system 102 of FIG. 1, supra, or alternatively it may be theplanning image where the physician has defined the planning coordinatesystem while creating the treatment plan. However, the scope of thepresent teachings is not so limited, and in other prefer embodiments thepre-acquired image data set may have been acquired using CBCT, MRI,ultrasound, or tomosynthesis imaging equipment located in a differentroom than the treatment vault or otherwise having a different frame ofreference than that of the IGRT apparatus.

FIG. 8B illustrates a layout of simplified conceptual versions of thevarious images involved in the method of FIG. 8A. Shown in simplifiedconceptual form is a pre-acquired image data set 802 of a body part B,the body part B including a target structure B1 (for example, a tumor)that is the subject of the desired application of the treatmentradiation beam, as well as certain sensitive non-target structures B2and B3 that should be avoided by the treatment beam. Adjacent thereto inFIG. 8B is a block 803 illustrating the various modalities that can beused to acquire the pre-acquired image data set 802. Importantly, it isto be appreciated that the pre-acquired image data set 802, as that termis used herein, can refer not only to the particular 3D image volumethat was acquired, but can alternatively refer to any expression orabstraction of that same information, such as DRRs or DRTs (digitallyreconstructed tomograph) generated from that 3D volume. The pre-acquiredimage data set 802 will have characteristics and artifacts unique to theparticular imaging modality and imaging geometry of the referenceimaging system 102.

Referring again to FIG. 8A, at step 854 an initial medical image dataset of the body part is acquired using the setup imaging system whilethe body part is in an initial treatment position relative to the IGRTapparatus. As discussed above, the body part is in the initial treatmentposition when the patient setup process is complete and just before thebeginning of the application of treatment radiation. For clarity ofdisclosure herein, the time “0” is used to refer to the time at whichthe body part is in the initial treatment position. Shown in simplifiedconceptual form in FIG. 8B is an initial medical image labeled“setup(0)” with numerical reference 804 that is representative of themedical image acquired by the setup imaging system at time 0. Withoutloss of generality, the initial medical image labeled “setup(0)” withnumerical reference 804 is referenced herein as the setup image data set804.

Also illustrated at the bottom of FIG. 8B for purposes of descriptivecomparison is a graphical representation labeled “actual(0)” and havingnumerical reference 808, which represents a true version of the actual,physical body part as it is actually positioned in the treatment room.Without loss of generality, the graphical representation labeled“actual(0)” and having numerical reference 808 is referenced herein asthe actual disposition 808 of the body part at time 0. Notably, theactual disposition 808 at time 0 is illustrated in the actual x-y-zcoordinate system of the treatment room (only the y-z coordinates areshown in the simplified 2D version of FIG. 8B), the pre-acquired imagedata set 802 is illustrated in the i-j-k coordinate system of thereference imaging system 102, and the setup image data set 804 isillustrated in a coordinate system x′-y′-z′ of the setup imaging system(which system has a precisely known geometrical relationship, such as bycalibration, to the x-y-z coordinate system of the treatment room). Asillustrated conceptually in FIG. 8B, the setup image data set 804 willhave characteristics and artifacts unique to the particular imagingmodality and imaging geometry of the setup imaging system, which willgenerally be different than the characteristics and artifacts of thepre-acquired image data set 802. Adjacent to the setup image data set804 in FIG. 8B is a block 805 illustrating the various modalities (e.g.,CBCT, ultrasound, stereo 2D x-ray) that can be used to acquire the setupimage data set 804, as well as the various abstractions (e.g., DRRs orDRTs) with which the setup image data set 804 can be represented.

Referring again to FIG. 8A, at step 856 a first registration between theinitial medical image data set (i.e., the setup image data set 804) andthe pre-acquired image data set 802 is performed. For one preferredembodiment, the registration process is separable into (i) computationof a coordinate transformation associated with imaging geometry and/orreference frame differences between the two imaging systems, and (ii)computation of a first alignment variation or position variationassociated with underlying anatomical and/or positional variations ofthe body part between the times of acquisition.

FIG. 8C illustrates the simplified conceptual image versions of FIG. 8Btogether with simplified graphical representations of transformations“T” associated with selected registrations therebetween to be performedaccording to one or more of the preferred embodiments. Thus, illustratedin FIG. 8C is a transformation T_(PO) associated with a registrationbetween the pre-acquired image data set 802 and the setup image data set804.

At step 858, an initial tomosynthesis image data set of the body part isacquired using the tomosynthesis imaging system. Shown in simplifiedconceptual form in FIG. 8B is an image labeled “tomo(0)” with numericalreference 806 that is representative of a reconstructed version of thetomosynthesis image data acquired by the tomosynthesis imaging system attime 0, and which without loss of generality is referenced herein as theinitial tomosynthesis image data set tomo(0). The initial tomosynthesisdata set tomo(0) is illustrated in FIG. 8B in a coordinate systemx″-y″-z″ of the tomosynthesis imaging system (which coordinate system iscalibrated to the treatment room coordinate system x-y-z). Asillustrated conceptually in FIG. 8B, the initial tomosynthesis imagedata set tomo(0) will have characteristics and artifacts unique to thetomosynthesis imaging modality and the particular imaging geometry ofthe tomosynthesis imaging system, which will generally be different thanthe characteristics and artifacts of the pre-acquired image data set 802and, in the general case, will also be different than thecharacteristics and artifacts of the setup image data set 804.Advantageously, there is an intrinsic, inherent registration providedbetween the setup image data set 804 and the initial tomosynthesis imagedata set tomo(0) by virtue of the precisely known geometries of theiracquisition systems relative to each other and by virtue of the set upand tomo(0) images being acquired close in time preferably such theposition of the target and other objects of interest have notappreciably moved between image acquisition; this inherent registrationmaking a transformation T_(0-t0) therebetween relatively straightforwardto implement even when the data sets are from different modalities.

Referring again to FIG. 8A, at step 860 a subsequent tomosynthesis imagedata set, i.e., an intrafraction tomosynthesis data set, is acquiredusing the tomosynthesis imaging system. Shown in FIG. 8B are examples ofa subsequent tomosynthesis data set tomo(t1) which reflects, albeit inits heavily artifact-laden tomosynthesis manner, deformations andpositional variations in the body part that occurred between time 0 andtime t1. These deformations and positional variations are shownconceptually therebelow in FIG. 8B by the actual disposition 808 at timet1. At step 862, a second registration between the subsequenttomosynthesis image data set tomo(t1) and the initial tomosynthesisimage data set tomo(0) is performed. Shown in FIG. 8C is atransformation T_(t0-t1) associated with this second registration.Advantageously, because the subsequent tomosynthesis image data settomo(t1) will have most if not all the same characteristics andartifacts as the initial tomosynthesis image data set tomo(0), thisregistration process is extremely fast and straightforward, very quicklyyielding the underlying anatomical and/or positional variations of thebody part between times 0 and t1 with respect to the x″-y″-z″ frame ofreference of the tomosynthesis imaging system.

Finally, at step 864 treatment radiation is delivered to the body partbased at least in part on information derived from (i) the firstregistration between the initial medical image data set (setup imagedata set 804) and the pre-acquired image data set 802 (see FIG. 8C,transformation T_(PO)), (ii) the inherent registration between theinitial tomosynthesis image data set tomo(0) and the initial medicalimage data set (setup image data set 804) (see FIG. 8C, transformationT_(O-t0)), and (iii) the second registration between the subsequenttomosynthesis image data set tomo(t1) and the initial tomosynthesisimage data set tomo(t0) (see FIG. 8C, transformation T_(t0-t1)). Theprocess can then be repeated for a subsequent tomosynthesis image dataset tomo(t2) and each subsequent tomosynthesis image data set acquiredthereafter during the treatment fraction. For one preferred embodiment,using the intrafraction time t1 as an example, the delivery of thetreatment radiation comprises computing a third registration betweentomo(t1) and the pre-acquired image data set 802 (see FIG. 8C,transformation T_(P-t1)) based on a serial application of the secondregistration (see FIG. 8C, transformation T_(t0-t1)), the inherentregistration between the initial tomosynthesis image data set tomo(0)and the setup image data set 804 (see FIG. 8C, transformation T_(O-t0)),and the first registration (see FIG. 8C, transformation T_(PO)), asreflected in box 813 of FIG. 8C.

Also shown in FIG. 8C for purposes of illustration is an exemplarytreatment beam RAY_(PLANNED) that was computed by the treatment planningsystem prior to the treatment fraction based on the pre-acquired imagedata set 802. For purposes of this very simple example, it is presumedthat the treatment plan consists of a single, stationary radiation beamRAY_(PLANNED) that persists throughout the treatment fraction and whichimpinges upon the treatment target B1 without passing through sensitivenon-target structures B2 and B3. As illustrated near the bottom of FIG.8C, at time 0 the fraction begins with the actual treatment beamRAY_(ACTUAL)(0) which is determined for the actual IGRT coordinate spacebased on the first registration between the initial medical image dataset (setup image data set 804) and the pre-acquired image data set 802(see FIG. 8C, transformation T_(PO)), as reflected in box 811 of FIG.8C. As of time t2, an actual treatment beam RAY_(ACTUAL)(t2) is beingapplied, which has been determined for the actual IGRT coordinate spacebased on a serial application of the relevant second registration (seeFIG. 8C, transformation T_(t0-t2)), the inherent registration betweenthe initial tomosynthesis image data set tomo(0) and the setup imagedata set 804 (see FIG. 8C, transformation T_(O-t0)), and the firstregistration (see FIG. 8C, transformation T_(PO)), as reflected in box815 of FIG. 8C.

Advantageously, the relatively difficult and time-consuming registrationbetween the initial medical image data set (setup image data set 804)and the pre-acquired image data set 802 (see FIG. 8C, transformationT_(PO)) does not need to take place during the treatment fraction afterthe beginning of radiation delivery, and only the very quickregistrations between each subsequent tomosynthesis image data sets(tomo(t1), tomo(t2), and so forth) and the initial tomosynthesis imagedata tomo(0) needs to take place during the treatment fraction after thebeginning of radiation delivery, thereby promoting at least one ofreduced intra-fraction computational intensity and reduced treatmentradiation delivery margins. Stated differently, the method of FIG. 8Aprovides an advantage that registrations between image data setscorresponding to different frames of reference do not require repeatedcomputation throughout the radiation treatment fraction, therebypromoting at least one of reduced intra-fraction computational intensityand reduced treatment radiation delivery margins.

As illustrated by the box 807 in FIG. 8B, any of a wide variety of x-raytomosynthesis acquisition methodologies and geometries can be used inconjunction with the method of FIG. 8A. Examples include the use ofx-ray source arrays (see, for example, FIGS. 4-5, supra) or translatedx-ray point sources (see, for example, FIG. 2, supra). Further examplesinclude the use of a single tomosynthesis imaging arc (see, for example,FIG. 2, supra), stereoscopic implementations using dual tomosynthesisimaging arcs (see, for example, FIGS. 4-5, supra), and otherimplementations using three or more tomosynthesis imaging arcs.Stereoscopic tomosynthesis implementations such as those of FIGS. 4-5supra can be particularly advantageous, each channel separatelyproviding three-dimensional information that is somewhat reduced inresolution in a direction away from its source array, but that reducedresolution being at least partially compensated by virtue of thepresence of image information from the other channel taken along asubstantially different tomosynthesis imaging arc.

FIG. 9A illustrates image guided radiation treatment of a body part byan IGRT apparatus according to another preferred embodiment that issimilar in certain respects to the preferred embodiment of FIG. 8A,except that the tomosynthesis imaging system of the IGRT apparatus isalso used as the setup imaging system. The method of FIG. 9A can bereadily understood in view of the steps shown thereon and in view ofFIGS. 9B-9C as shown. The method of FIG. 9A can be implemented, forexample, using any of the IGRT systems of FIGS. 3-6, supra, and moregenerally any IGRT system that includes a kV x-ray tomosynthesis imagingcapability. At step 952 a pre-acquired image data set of the body partis received, the pre-acquired image data set having been acquired in areference frame generally independent of the reference frame of the IGRTapparatus (see FIG. 9A, pre-acquired image data set 902). As illustratedat block 903 of FIG. 9B, the pre-acquired image data set 902 may havebeen acquired using conventional CBCT, MRI, ultrasound, or tomosynthesisimaging equipment located in a different room than the treatment vaultor otherwise having a different frame of reference than that of the IGRTapparatus. At step 954 an initial tomosynthesis medical image data setof the body part is acquired using the tomosynthesis imaging systemwhile the body part is in an initial treatment position relative to theIGRT apparatus (see FIG. 9B, initial tomosynthesis image data settomo(0)). As illustrated by the box 905 in FIG. 9B, any of a widevariety of x-ray tomosynthesis acquisition methodologies and geometriescan be used including, but not limited to, the use of x-ray sourcearrays, translated x-ray point sources, a single tomosynthesis imagingarc, stereoscopic implementations using dual tomosynthesis imaging arcs,other implementations using three or more tomosynthesis imaging arcs,single-energy x-ray tomosynthesis imaging, dual-energy x-raytomosynthesis imaging, and multiple x-ray energy tomosynthesis imaging.At step 956, a first registration between the initial tomosynthesisimage data set tomo(0) and the pre-acquired image data set 902 isperformed (see FIG. 9C, transformation T_(P-t0)). At step 958 asubsequent tomosynthesis image data set, i.e., an intrafractiontomosynthesis data set, is acquired using the tomosynthesis imagingsystem (see FIG. 9B, tomo(t1)). At step 960 a second registrationbetween the subsequent tomosynthesis image data set tomo(t1) and theinitial tomosynthesis image data set tomo(0) is performed (see FIG. 9Cis a transformation T_(t0-t1)). At step 962 treatment radiation isdelivered to the body part based at least in part on information derivedfrom (i) the first registration between the initial tomosynthesis imagedata set tomo(0) and the pre-acquired image data set 902 (see FIG. 9C,transformation T_(P-t0)), and (ii) the second registration between thesubsequent tomosynthesis image data set tomo(t1) and the initialtomosynthesis image data set tomo(t0) (see FIG. 9C, transformationT_(t0-t1)). The process can then be repeated for a subsequenttomosynthesis image data set tomo(t2) and each subsequent tomosynthesisimage data set acquired thereafter during the treatment fraction. Forone preferred embodiment, using the intrafraction time t1 as an example,the delivery of the treatment radiation comprises computing a thirdregistration between tomo(t1) and the pre-acquired image data set 902(see FIG. 9C, transformation T_(P-t1)) based on a serial application ofthe second registration (see FIG. 9C, transformation T_(t0-t1)) and thefirst registration (see FIG. 9C, transformation T_(P-t0)), as reflectedin box 913 of FIG. 9C. As illustrated near the bottom of FIG. 9C, attime 0 the fraction begins with the actual treatment beamRAY_(ACTUAL)(0) which is determined for the actual IGRT coordinate spacebased on the first registration between the initial tomosynthesis imagedata set tomo(0) and the pre-acquired image data set 902 (see FIG. 9C,transformation T_(P-t0)), as reflected in box 911 of FIG. 9C. As of timet2, an actual treatment beam RAY_(ACTUAL)(t2) is being applied, whichhas been determined for the actual IGRT coordinate space based on aserial application of the relevant second registration (see FIG. 9C,transformation T_(t0-t2)) and the first registration (see FIG. 9C,transformation T_(P-t0)), as reflected in box 915 of FIG. 9C. Similar tothe preferred embodiment of FIG. 8A, there is an advantage provided inthat the relatively difficult and potentially time-consumingregistration between the initial tomosynthesis image data set tomo(0)and the pre-acquired image data set 902 does not need to take placeafter the beginning of radiation delivery when time is of the essence,and instead is only required at time prior to the beginning of radiationdelivery when time performance is less of an issue. During the treatmentfraction after the beginning of radiation delivery, it is only the veryquick and precise registrations between each subsequent tomosynthesisimage data set (tomo(t1), tomo(t2), etc.) and the initial tomosynthesisimage data tomo(0) that need to take place. At least one of reducedintra-fraction computational intensity and reduced treatment radiationdelivery margins is promoted. As with the preferred embodiment of FIG.8A, it is to be appreciated that the registration between the initialtomosynthesis image data set tomo(0) and the pre-acquired image data set902 can be performed using a purely 3D version of the pre-acquired imagedata set 902, or using any of a rich variety of different expressions orabstractions based on the pre-acquired image data set 902 (e.g., DRRsand DRTs) without departing from the scope of the preferred embodiments.In one of many different examples, the registration can be of a tomo(0)volume to a DRT volume derived from a 3D version of the pre-acquiredimage data set 902, comprising the steps of identifying a first imageslice within the DRT image volume for which an anatomical object ofinterest is in focus, identifying a second image slice within thetomo(0) volume for which the anatomical object of interest is in focus,and then performing a 2D-2D registration between said first and secondimage slices. In another example, there can be a pure 3D-3D registrationbetween the DRT image volume and the tomo(0) volume. In still anotherexample, there can be a pure 3D-3D registration between a pure 3Dversion of the pre-acquired image data set 902 (i.e., not a DRTabstraction) and the tomo(0) volume.

FIG. 10 illustrates a tomosynthesis imaging system 1000 as may beintegrated into one or more of the above-described IGRT systemsaccording to a preferred embodiment, the tomosynthesis imaging system1000 providing dual-energy stereoscopic tomosynthesis imaging accordingto a preferred embodiment. Tomosynthesis imaging system 1000 comprisesdual x-ray source arrays SA1 and SA2 and dual detectors D1 and D2. Forthe preferred embodiment of FIG. 10 and all subsequent preferredembodiments described hereinbelow, it is to be appreciated that althoughmultiple adjacent and/or nearby x-ray source arrays may be illustratedas distinct physical components for clarity of presentation, they can bephysically integrated into a common substrate or otherwise physicallyconnected or coupled to form a common physical source device. Likewise,it is to be appreciated that although multiple adjacent and/or nearbydetector arrays may be illustrated as distinct physical components forclarity of presentation, they can also be physically integrated into acommon substrate or otherwise physically connected or coupled to form acommon physical detector device. Source array SA1 and detector array D1are configured, dimensioned, and positioned to provide a first x-raytomosynthesis source-detector pair SA1-D1, i.e., a source-detector paircapable of acquiring two or more x-ray tomosynthesis projection imagesat two or more respective tomosynthesis projection angles. Source arraySA2 and detector array D2 are likewise configured, dimensioned, andpositioned to provide a second x-ray tomosynthesis source-detector pairSA2-D2. Preferably, the first and second source-detector pairs aremutually arranged in a generally stereoscopic arrangement relative tothe target volume such as shown in FIG. 10.

Dual-energy imaging is a technique that can be used to improve thevisibility of masked tissue in X-ray based imaging, and utilizes X-rayemissions having different energy spectra or profiles. X-ray images maybe acquired of a patient or portion of a patient using two differentX-ray energy profiles, one at a relatively high energy (e.g., 140 kV)and one at a relatively low energy (e.g., 80 kV), such that a differentset of image data is acquired for each energy profile. The differentsets of image data, when processed, may be used to construct differentimages that characterize the density or attenuating characteristics ofthe imaged volume. By decomposing the acquired image data, images mayalso be generated which differentially reflect the composition of theimaged volume, such as bone or soft tissue.

Provided according to one preferred embodiment is an image-guidedradiation treatment (IGRT) apparatus including the first and secondx-ray tomosynthesis source-detector pairs (SA1-D1, SA2-D2) positioned toacquire tomosynthesis projection images over first and second projectionangle ranges, respectively, that are non-overlapping with each other.First and second sets of tomosynthesis projection images of the targetvolume are acquired at distinct first and second x-ray energy levels,respectively (e.g., 80 kV and 140 kV), using the respective first andsecond x-ray tomosynthesis source-detector pairs.

The first and second sets of tomosynthesis projection images are thenprocessed to generate respective first and second tomosynthesisreconstructed image sets of the target volume. Any of a variety ofdifferent tomosynthesis reconstruction algorithms can be used including,but not limited to, filtered backprojection (FBP), matrix inversiontomosynthesis (MITS), maximum likelihood expectation maximization(MLEM), and iterative ordered-subset convex (OSC) algorithms based on amaximum-likelihood models.

The first and second tomosynthesis reconstructed image sets are thenprocessed in conjunction with each other on a locationwise basis (e.g.,voxelwise basis) within the target volume to generate a dual-energyprocessed image set. For one preferred embodiment, the processing of thefirst and second tomosynthesis reconstructed image sets comprisesregistration (either by a known physical transformation between theimaging coordinate spaces or by image-based registration) andsubtraction processing and/or other decomposition into soft-tissue andbone image components. Treatment radiation is delivered to the treatmenttarget within the target volume based at least in part on thedual-energy processed image set.

For one preferred embodiment, the array sources SA1 and SA2 areconstructed and/or modified to include a source collimation capabilitysuch that no primary x-ray passing through the target volume from thefirst source SA1 impinges upon the second detector D2, and no primaryx-ray passing through the target volume from the second source SA2impinges upon the first detector D1. Advantageously, the first andsecond sets of tomosynthesis projection images can then be acquiredsimultaneously, thereby reducing imaging time and reducing thepossibility the target volume moves in between image acquisition.

For one preferred embodiment, the first and second sets of tomosynthesisprojection images are simultaneously, or substantially simultaneously,acquired at periodic intervals corresponding to a common phase of aphysiological movement cycle of the patient (e.g., a respiratory cycleor a heartbeat cycle), and the IGRT apparatus is further equipped with anon-x-ray-based movement sensing system that processes continuouslymonitored external patient movement data in conjunction with acorrelation model to predictively compute target volume movement duringthe physiological movement cycle. The dual-energy processed image set isused to update the correlation model at each acquisition cycle.

Optionally, the source arrays SA1 and SA2 can each alternate betweenlow-energy and high-energy emission modes at respective periodic imagingcycles. For one preferred embodiment, the source arrays SA1 and SA2 canbe in-phase with each other (i.e., both emitting at low energy, thenboth emitting at high energy, etc.), while for another preferredembodiment, the source arrays SA1 and SA2 can be out of phase with eachother (i.e., one emitting at low energy while the other emits at highenergy).

Although dual-energy x-ray tomosynthesis has been found particularlyadvantageous in the context of the stereoscopic applications, the scopeof the present teachings is not so limited and includes alternativepreferred embodiments in which only a single tomosynthesis imaging arcis involved, either by virtue of using only a single x-ray source arrayor by virtue of using multiple x-ray source arrays that collectivelyextend over only a single tomosynthesis imaging arc. Moreover, for bothnon-stereoscopic and stereoscopic preferred embodiments, a variety ofdifferent methods of configuring and/or operating one or more of thex-ray sources is within the scope of the present teachings including,for example: (i) rapidly varying the electron accelerating potential ofeach of the x-ray sources between low voltage and high voltage modes toachieve respective low and high energy x-ray tomosynthesis projectionimages at closely spaced points in time; (ii) positioning dedicatedlow-energy x-ray sources and dedicated high-energy x-ray sourcesadjacently to each other along the x-ray source array and interleavingtheir operation on either (a) a per tomosynthesis imaging set basis(i.e., all projection angles at low energy, then all projection anglesat high energy), or (b) a per projection angle basis (i.e., a low-energyprojection image at a first angle followed by a high energy projectionimage at that first angle, then a low-energy projection image at asecond angle followed by a high energy projection image at that secondangle, and so on); and (iii) a combination of temporally interleavingand spatial interleaving of the x-ray source energies, for example, in amanner analogous to the discrete RGB emission sources of an LCD colordisplay.

Although applicable in a wide variety of medical imaging environments,the preferred embodiments described herein in relation to stereo andnon-stereo dual-energy tomosynthesis are particularly advantageous forapplication in radiation treatment environments where it is impossibleand/or unrealistic to expect a patient to temporarily “freeze” while aset of tomosynthesis projection images is acquired. For preferredembodiments in which the low-energy and high-energy tomosynthesisprojection images are acquired simultaneously, there is a furtheradvantage provided in that there is an intrinsic time registrationbetween them that, in conjunction with a spatial registrationestablished by virtue of the known imaging geometries involved, providesfor proper registration and feature alignment between the low and highenergy volumes, which in turn enables fast and accurate generation of adual energy processed data volume.

FIG. 11A illustrates selective collimation of x-ray emission from anx-ray source array according to a preferred embodiment. An x-ray sourcearray SA is provided with a linear, two-dimensional, and/orthree-dimensional arrangement of individually addressable anddynamically activatible x-ray sources S. For clarity of presentationherein, individual x-ray sources of an x-ray source array areillustrated simply by the location of their focal spot, as shown in FIG.11A. For some preferred embodiments, the individual x-ray sources S canbe referred to as x-ray source pixels. For clarity of presentation, manyof the preferred embodiments are graphically represented in the drawingsin the context of one-dimensional (linear) x-ray source arrays andassociated one-dimensional depictions of corresponding detector arrays.It is to be appreciated, however, that these representations are merelyillustrative and that the corresponding two-dimensional andthree-dimensional counterparts of these teachings are also embodiedwithin these descriptions as would be apparent to a person skilled inthe art in view of the present disclosure.

Also illustrated in FIG. 11A is a collimation device COLL comprising alight absorbing material, such as lead or tungsten, into which is formedapertures A that correspond respectively to the x-ray sources S. For onepreferred embodiment, each aperture A is configured and dimensioned toprovide a relatively narrow, fixed cone beam angle for its respectivesource that is incident upon a subregion R of the detector D. Eachcombination of source and aperture (S/A) can be called a “pixel” of thesource array SA. For another preferred embodiment, one or more of theapertures A can be actuated, such as by using microelectromechanicalsystems (MEMS) technology to vary the cone beam angle for that pixel,and/or to entirely block (turn off) and unblock (turn on) that pixel.Preferably, each S/A pixel of the source array SA can be individuallyaddressed and actuated. Alternatively, the pixels can be addressed andcontrolled on a groupwise basis. Without loss of generality hereinbelow,the activation/deactivation of a particular pixel of an x-ray sourcearray is described in terms of the addressable electricalactivation/deactivation of the corresponding x-ray source. However, itis to be appreciated that the activation/deactivation of one or more ofthe pixels of an x-ray source can alternatively be achieved by aMEMS-based blocking or unblocking of that source pixel without departingfrom the scope of the present teachings.

With exemplary non-limiting reference to FIG. 11A, provided in onepreferred embodiment is a method for reduced dosage x-ray imaging (or,alternatively, higher quality imaging for a predefined x-ray dose) of atarget structure T using an x-ray source array SA and an x-raycollimating device COLL. The x-ray collimating device COLL is configuredand dimensioned to individually collimate x-ray radiation from each of afirst plurality of x-ray sources S onto a corresponding subgroup ofdetector pixels covering an area R substantially smaller than thepredefined imaging area of the detector D. Thus, the x-ray collimatingdevice COLL is configured such that, for each x-ray source S in thesource array SA, there is a predetermined subregion R of detector pixelsthat will receive primary x-ray radiation therefrom. For this preferredembodiment, it is known that the target structure T will project onto arelatively small subregion of the imaging area of a detector D in viewof the size of the target volume and the overall imaging geometrypresented. Based on knowledge of the approximate location of the targetstructure T, only those x-ray sources S necessary to encompass thetarget structure T with respect to its projection onto the detector Dare activated. The digital detector D is selectively operated such thatonly the detector pixels corresponding to the currently activated x-raysource(s) are used to measure x-ray radiation. According to onepreferred embodiment, the knowledge of the location of the targetstructure T can be determined from previous medical images of thepatient in conjunction with current knowledge of the position of thepatient relative to the imaging geometry.

When compared to a prior art scenario in which a single x-ray sourcecovering the entire predefined imaging area is used to achievecomparable x-ray flux through the target, and assuming (as is often thecase) that there is patient anatomy generally surrounding the targetstructure T, the above-described preferred embodiment can provide asimilar-quality image at a substantial x-ray dose reduction.Alternatively, for a similar overall x-ray dose as would be applied tothe patient by the prior art single x-ray source, a higher-quality imagecan be obtained by increasing the power of the activated x-ray sourcesin the x-ray source array.

FIG. 11B illustrates selective collimation of x-ray emission from anx-ray source array according to another preferred embodiment. An x-raysource array SA and collimator COLL is provided with a first group ofpixels or source/aperture pairs S1/A1 that are similar in function tothe pixels or source/aperture pairs S/A of FIG. 11A, with each of themproviding a relatively narrow, fixed cone beam angle for its respectivesource that is incident upon a subregion R1 of the detector D. Alsoprovided is a second source S2 and corresponding aperture A2 mutuallyconfigured to illuminate a region R2 of the detector D that issubstantially larger than each subregion R1. The second source S2 canoptionally be termed a “pilot” source. For one optional preferredembodiment, the region R2 covers a substantial entirety of the imagingarea available on detector D. The device of FIG. 11B can be used in amethod for reduced dosage x-ray imaging (or, alternatively, higherquality imaging for a predefined x-ray dose) similar to the methoddescribed above in relation to FIG. 11A, with a further advantage thatthe x-ray source S2 can be operated prior to the x-ray source(s) S1 toacquire a “pilot image” of the overall target volume containing thetarget structure T. The pilot image can be a relatively low-qualityimage acquired with a very low x-ray dose, since it is only being usedto identify the general locality of the target structure T within thelarger target volume on the detector D. Thus, using the device of FIG.11B, it is no longer required to acquire a priori target volume locationfrom external data sources. In an alternative preferred embodiment,instead of using an added “pilot” x-ray source to initially localize thetarget structure, a plurality of the source array members S1 can beseparately operated one at a time, at very brief low-dose imagingintervals, to acquire a set of smaller “pilot” images that can beprocessed to identify the location of the target structure.

Also provided according to one or more preferred embodiments are methodsand systems for reduced-dosage and/or higher quality x-ray tomosynthesisimaging of a target structure contained within a target volume, based onan extension to tomosynthesis of the devices and methods described abovein relation to FIGS. 11A-11B. An x-ray tomosynthesis imaging source isprovided comprising a plurality of x-ray source array units disposed ata respective plurality of tomosynthesis projection angles relative tothe target volume, each x-ray source array unit comprising a firstplurality of x-ray sources spatially distinct from each other. Referringforward briefly to FIG. 17-1, an example of an x-ray tomosynthesisimaging source is shown that comprises five x-ray source array unitslabeled SAU1 through SAU5. Each x-ray source array unit SAU1-SAU5comprises a first plurality of x-ray sources S. Also provided is anx-ray tomosynthesis imaging detector comprising a plurality of digitaldetector units respectively disposed opposite the plurality of x-raysource array units relative to the target volume, each digital detectorunit being thereby paired with a corresponding one of the x-ray sourcearray units, each digital detector unit comprising an array of detectorpixels extending over a predefined imaging area. Referring forwardbriefly to FIG. 17-1, an example of an x-ray tomosynthesis imagingdetector is shown that comprises five digital detector units labeledDDU1 through DDU5. Provided in association with each x-ray source arrayunit is an x-ray collimating unit disposed between that x-ray sourcearray unit and the target volume, the x-ray collimating unit beingpositioned closer to that x-ray source array unit than to the targetvolume, the x-ray collimating unit being configured and dimensioned toindividually collimate x-ray radiation from each of the first pluralityof x-ray sources of that x-ray source unit onto a corresponding subgroupof detector pixels of the paired digital detector unit that cover anarea substantially smaller than the predefined imaging area of thepaired digital detector unit. Referring forward briefly to FIG. 17-1,there are shown five x-ray collimating units labeled XCU1 through XCU5.

For this tomosynthesis-related preferred embodiment, it is known thatthe target structure will project onto a relatively small subregion ofthe imaging area of each digital detector unit in view of the size ofthe target structure within the target volume and the overall imaginggeometry presented. Based on knowledge of the location of the targetstructure within the target volume, only particular ones of the firstplurality of x-ray sources of each x-ray source array unit necessary toencompass the target structure with respect to its projection onto thepaired digital detector unit are activated. Each digital detector unitis selectively operated such that only the detector pixels correspondingto the currently activated x-ray source(s) of the corresponding x-raysource array are used to measure x-ray radiation. According to onepreferred embodiment, the knowledge of the location of the targetstructure within the target volume can be determined from previousmedical images of the patient in conjunction with current knowledge ofthe position of the patient relative to the imaging geometry.

According to another preferred embodiment, a previously acquiredlow-dose “pilot” tomosynthesis image set is used to localize the targetstructure. More particularly, provided on each of the x-ray source arrayunits is an additional x-ray source distinct from the first plurality ofx-ray sources, and the associated x-ray collimating unit is configuredto collimate x-ray radiation from the additional x-ray source onto asubstantial entirety of the predefined imaging area of the paireddigital detector unit. At a previous time interval, the plurality ofx-ray source array units and the corresponding digital detector unitsare operated to acquire a plurality of “pilot” tomosynthesis projectionimages of the target volume within which the target structure isdisposed. In acquiring the “pilot” tomosynthesis projection images, onlythe additional x-ray source of each x-ray source array unit is operated.The “pilot” tomosynthesis projection images are then processed tolocalize the target structure within the target volume.

FIGS. 11C-11D conceptually illustrate two-dimensional imaging andtracking of a target according to a preferred embodiment using, by wayof example, the two-dimensional x-ray imaging apparatus of FIG. 11B. Atstep 1102, a pilot image is acquired using the pilot x-ray source S2,and the pilot image is processed to identify a target-containingsubregion of the detector. At step 1104, the target is dynamicallytracked using localized projection imaging from individual ones of thex-ray sources S1. A variety of different segmentation and predictivelocation estimation algorithms can be used to predict where the targetstructure T will be relative to the detector D, and to thereby selectwhich of the sources S1 to activate at any particular imaging interval.As an alternative to pilot imaging using the source S2, the sources S1can be sequentially activated, one at a time, to acquire a set ofsmaller pilot images that can be processed to identify the initiallocation of the target structure.

FIG. 12A illustrates an x-ray source collimation device COLL and anx-ray source array SA according to a preferred embodiment. Thecollimation device COLL comprises a plurality of slat-like louvers Larranged in parallel fashion over the x-ray source array SA, each pairof louvers L forming a thin collimating slab that directs x-rayradiation in the direction of the thin slab. The louvers L are formedfrom an x-ray opaque material such as tungsten. For the preferredembodiment of FIG. 12A, the louvers L are directed normal to an emissionsurface of the source array SA, collimating the generally isotropicx-rays emitted from the x-ray sources S into thin slabs parallel to thex-z plane. To collimate the x-rays into a strictly vertical direction(the “x” direction of FIG. 12A), a second array of similarly constructedlouvers parallel to the x-y plane is stacked atop the arrangement ofFIG. 12A. For one preferred embodiment, both layers of louvers L arefixably disposed in predetermined directions, while for anotherpreferred embodiment, one or both of the layers has an adjustabledirection.

FIG. 12B illustrates an x-ray source collimation device COLL and anx-ray source array SA according to a preferred embodiment in which thex-ray beams are dynamically steered according to actuation of thedirection of the louvers L. Any of a variety of control and actuationmechanisms (not shown) can be used to manipulate the collimation angleincluding, but not limited to, motor-driven mechanical rods and hinges,electrostatic or magnetostatic actuation schemes, and various othermechanical, electrical, and/or microelectromechanical (MEMS) basedactuation schemes.

FIG. 13 illustrates a simplified perspective view of an x-ray sourcecollimation device COLL and an x-ray source array SA according to apreferred embodiment, the collimation device COLL comprising a firststeerable louver array LX and a second steerable louver array LY. Thecollimation device COLL is designed to collimate the x-ray radiationinto a population of substantially parallel x-ray pencil beams,preferably such that each primary ray impinges upon the detector at thesame angle of incidence. A rich variety of strategic illumination andimaging schemes are enabled by virtue of the population of parallelpencil beams that can reduce x-ray imaging dose and/or increase imagequality, particularly when the beams are simultaneously steerable andwhen each beam is individually activated by one or more separateelectronic activation signals. Moreover, distortion artifactstraditionally associated with single-point x-ray sources due tospreading of the beam are avoided.

Because it functions by absorption of x-ray photons that are not emittedin the aimed direction, which is on the order of 99% of all emittedx-ray photons, the collimation device COLL is not necessarily efficientin the sense of overall power requirements, and the device willfurthermore operate at relatively high temperatures that may requireforced air or liquid cooling systems. However, in terms of x-ray dose tothe patient, the collimation device COLL is highly efficient, with thesurviving pencil-beam x-ray photons being judiciously aimed at theregion of the particular target structure of interest within thepatient.

For one preferred embodiment, the collimating device COLL is similar inmaterials and construction to one or more single photon emissioncomputed tomography (SPECT) collimators disclosed in U.S. Pat. No.7,345,282B2, which is incorporated by reference herein. However, theSPECT collimators disclosed in U.S. Pat. No. 7,345,282B2 areincorporated into a substantially different environment thantwo-dimensional x-ray imaging and x-ray tomosynthesis imaging, andfurthermore are detector-mounted collimators rather than source-mountedcollimators.

For one preferred embodiment, the spatial separation of the arrayedlouvers L corresponds directly to the spacings of x-ray sources S, andeach source S is disposed midway between respective louvers L in eachspatial direction, which is shown in one dimension (the y-direction) inFIGS. 12A-12B. By way of example only and not by way of limitation,x-ray source array SA may be characterized by an average x-ray sourcefocal spot size of 250 μm and an average focal spot spacing of about 1mm. For this case, the louvers L will likewise be spaced apart by 1 mm,may each have a thickness of about 0.2 mm, and may each have a height ofabout 5 cm. For another preferred embodiment, the x-ray source array SAmay be characterized by an average x-ray source focal spot size of 400μm and an average focal spot spacing dF in the range of 0.5 mm and 2 mm,and the louvers L may be spaced apart by dF, may each have a thicknessdimension of between about 0.1 mm and 0.3 mm, and may each have a heightin the range of 4 cm-8 cm. In other preferred embodiments, there may bean x-ray source located only at every second or third inter-louver gap(or generally every Nth inter-louver gap) so that there are no overlapsbetween respective illumination regions of the digital detector.

FIG. 14 illustrates a smaller scale (i.e., less detailed) conceptualside view of an x-ray source array SA and collimator COLL according to apreferred embodiment, wherein the collimator COLL is segmented into anumber of separately controlled segments COLSEG1, SOLSEG2, COLSEG3, andso on. In the illustration of FIG. 14, individual x-ray sources in thesource array SA and individual louvers in the collimator COLL are notillustrated, it being understood that there is a generally a largepopulation of each of them per unit distance. The individual segmentsCOLSEG can be a variety of different shapes and sizes, and can rangefrom association with a single x-ray source (i.e., aligned with a singlex-ray source focal spot) to hundreds or even thousands of x-ray sourceswithout departing from the scope of the present teachings. Moreover,there can be anywhere from a single segment COLSEG to tens, hundreds, oreven thousands of such segments distributed across the emitting surfaceof the source array SA without departing from the scope of the presentteachings. In one preferred embodiment, the collimation direction ofeach segment COLSEG is separately controlled, each segment thereby beingoperable as an independent “floodlight” that can be independently aimedin a desired direction. By virtue of the combination of (i)independently steerable collimation segments, together with (ii)independently controllable x-ray sources throughout the source array, avery large and rich variety of controlled target illumination scenariosare made possible, each of which is within the scope of the preferredembodiments.

FIGS. 15-16 each illustrate reduced dosage x-ray imaging (or higherquality imaging for a predefined x-ray dose) and target tracking of atarget structure T using an x-ray source array SA and an x-raycollimating device COLL according to a preferred embodiment. As would beappreciated by a person skilled in the art in view of the presentdisclosure, FIGS. 15-16 represent but two examples of a large number ofdifferent imaging/tracking scenarios that are made possible using x-raysource arrays having individual source control and collimating deviceshaving segmentwise directional control according to one or more of thepreferred embodiments. For each of the examples of FIGS. 15-16, a lowdose “pilot” image is first obtained by illuminating the entire imagingarea of the detector with parallel x-ray pencil beams. The low dose canbe achieved, for example, by only activating every second, third, orN^(th) x-ray source in the x-ray source array SA. In the example of FIG.15, the target structure T is tracked by virtue of non-steered x-raypencil beams that are selectively activated on a segmentwise basisacross the x-ray source array SA. In the example of FIG. 16, the targetstructure T is tracked by virtue of a combination of selectivesegmentwise x-ray source activation and active steering of the x-raypencil beams.

FIG. 17-1 through FIG. 17-5 illustrate acquiring a set of x-raytomosynthesis projection images of a target volume according to apreferred embodiment. Provided is an x-ray tomosynthesis imaging sourcecomprising a plurality of x-ray source array units SAU1-SAU5 disposed ata respective plurality of tomosynthesis projection angles relative tothe target volume, each x-ray source array unit SAU comprising a firstplurality of x-ray sources S spatially distinct from each other. Alsoprovided is an x-ray tomosynthesis imaging detector comprising aplurality of digital detector units DDU1-DDU5 respectively disposedopposite the x-ray source array units SAU1-SAU5 relative to the targetvolume, each digital detector unit DDU being thereby paired with acorresponding one of the x-ray source array units SAU, each digitaldetector unit comprising an array of detector pixels extending over apredefined imaging area. Also provided in association with the x-raysource array units SAU1-SAU5 is a respective set of x-ray collimatingunits XCU1-XCU5, each x-ray collimating unit XCU being disposed betweenits associated x-ray source array unit SAU and the target volume, eachx-ray collimating unit XCU being positioned closer to that x-ray sourcearray unit SAU than to the target volume. Each x-ray collimating unitXCU is configured and dimensioned to collimate x-ray radiation from itsrespective x-ray source unit SAU onto the paired digital detector unitDDU.

For the example of FIG. 17-1 through FIG. 17-5, a set of five (5)tomosynthesis projection images are acquired by respective activation ofthe five SAU-DDU pairs. It is to be appreciated that as few as twoSAU-DDU pairs and as many as 1000 SAU-DDU pairs can be provided, foracquiring 2-1000 tomosynthesis projection images, without departing fromthe scope of the present teachings. Although illustrated in FIG. 17-1through FIG. 17-5 as being non-overlapping with each other, in otherpreferred embodiments neighboring ones of the digital detector unitsDDU1-DDU5 can be overlapping with each other (i.e., can share one ormore digital detector pixels).

FIG. 18 illustrates acquiring a set of x-ray tomosynthesis projectionimages of a target volume according to a preferred embodiment in which(i) the digital detector units DDU1-DDU5 are non-overlapping with eachother, and (ii) the x-ray source array units SAU and x-ray collimatingunits XCU are configured such that each separate x-ray source array unitilluminates only its paired digital detector unit DDU with primaryx-rays, with no spillover of primary x-rays onto neighboring digitaldetector units. Advantageously, for this preferred embodiment, all ofthe x-ray tomosynthesis projection images can be acquiredsimultaneously, which can be particularly useful for dynamic targettracking when used in conjunction with the radiation treatment system ofFIG. 1, supra.

FIG. 19-1 through FIG. 19-5 illustrate acquiring a set of x-raytomosynthesis projection images of a target structure T according to apreferred embodiment. The target structure T can be, for example, atarget tumor needing treatment radiation that is positioned off-centerrelative to the tomosynthesis imaging system. Each x-ray sourcearray/x-ray collimating unit pair (SAU/XCU) is configured to be capableof a first mode of operation in which x-ray radiation is adjustablycollimated onto only a subgroup of detector pixels (i.e., only a portionof a predefined imaging area) of the paired digital detector unit DDU.Information is received that is indicative of the position of a targetstructure T, for example by virtue of a low-dose “pilot” tomosynthesisdata set acquired using a second mode of operation similar to that ofFIG. 18, supra. The x-ray source array units SAU are sequentiallyactivated to acquire a set of x-ray tomosynthesis projection images.However, for each x-ray source array unit SAU, only the particularsubgroup of x-ray sources whose projections onto the paired digitaldetector unit DDU are necessary to laterally encompass the targetstructure T are activated. The identity of the necessary subgroup ofx-ray sources can be readily determined from the low-dose “pilot”tomosynthesis data set. Methods for generating tomosynthesisreconstructed image data from the x-ray tomosynthesis projections ofFIG. 19-1 through FIG. 19-5 would be apparent to a person skilled in theart in view of the present disclosure.

FIG. 20 illustrates acquiring a set of x-ray tomosynthesis projectionimages of a target volume according to a preferred embodiment similar tothat of FIG. 19-1 through FIG. 19-5, except that all of the x-raytomosynthesis projection images are acquired simultaneously.Advantageously, when compared to a scenario in which each x-ray sourceunit comprises a single x-ray source that illuminates the entirepredefined imaging area of the paired digital detector unit, thepreferred embodiments of FIG. 19-1 through FIG. 19-5 and FIG. 20 canprovide a similar-quality image at a substantial x-ray dose reduction.Alternatively, for a similar overall x-ray dose as would be applied tothe patient by the single-source units, a higher-quality image can beobtained by increasing the power of the activated x-ray sources in thex-ray source array. In yet another alternative, for a similar overallx-ray dose as would be applied to the patient by the single-source unitsand for a similar image quality, the time rate of capture of respectivex-ray tomosynthesis data sets can be increased (for example, acquiringan x-ray tomosynthesis data set every 5 seconds rather than every 15seconds) for providing improved temporal accuracy in target tracking.

FIG. 21-1 through FIG. 21-5 illustrates acquiring a set of x-raytomosynthesis projection images of a target volume according to apreferred embodiment that is functionally similar to that of FIG. 19-1through FIG. 19-5, except that the selective localized illumination ofdigital detectors is achieved by mechanical control of the beamsteeringangle of the x-ray collimating units XCU while the subset of x-raysources within each x-ray source array unit SAU is kept constant. FIG.22 illustrates acquiring a set of x-ray tomosynthesis projection imagesof a target volume according to a preferred embodiment similar to thatof FIG. 21-1 through FIG. 21-5, except that all of the x-raytomosynthesis projection images are acquired simultaneously. Any of avariety of different combinations of selective target illuminationconfigurations and strategies, as exemplified by FIG. 19-1 through FIG.22, can be used and are within the scope of the present teachings.

FIGS. 23A-23D illustrate an inverse geometry tomosynthesis imagingsystem 2301 that can be used in tomosynthesis imaging according to apreferred embodiment. Inverse geometry tomosynthesis imaging system 2301comprises a digital detector array 2302, an x-ray source array 2304having a collimation device 2306 closely positioned therenear orintegral therewith. The digital detector array 2302 is positionedopposite the x-ray source array 2304 and collimation device 2306relative to the target volume V, which includes a target structure T.Preferably, the x-ray source array comprises a computer-steerableelectron beam and a spatial arrangement of metallic targets, eachmetallic target becoming an active x-ray focal spot when the electronbeam is steered onto it, such as one or more such devices developed byTriple Ring Technologies, supra. However, other types of x-ray sourcearrays, such as cold-cathode source arrays, can alternatively be used.

In one preferred embodiment, the inverse geometry tomosynthesis imagingsystem 2301 can be implemented in conjunction with the robotic arm-basedIGRT system 400 of FIG. 4, supra, with the x-ray source array 2304taking the position of x-ray source array 406 and the digital detectorarray 2302 taking the position of the detector array 412. In oneexample, the x-ray source array 2304/406 can be positioned in or nearthe floor of the treatment vault, positioned beneath the treatment couchC by about 0.5 m-1.0 m, while the digital detector array 2302/412 can bepositioned in or near the ceiling of the treatment vault, positionedabove the treatment couch C by about 1.0 m-2.0 m. In another preferredembodiment, further to the configuration of FIG. 4, supra, there are twosimilar inverse geometry tomosynthesis imaging systems provided that areoriented in a stereoscopic configuration relative to the treatmentvolume, the first being implemented by the source/detector pair 406/412and the second being implemented by the source/detector pair 408/410.Optionally, the two inverse geometry tomosynthesis imaging systems canhave different x-ray energies (e.g., 80 keV and 140 keV, respectively)for providing a dual-energy capability. In another preferred embodiment,the arrangement of FIG. 5 is used in which the stereoscopic angle issubtended along the head-to-toe direction of the treatment couch C. Forclarity of disclosure, only a single inverse geometry tomosynthesisimaging system 2301 is illustrated in the example of FIGS. 23A-23D.

The inverse geometry tomosynthesis imaging system 2301 is characterizedin that the digital detector array 2302 is smaller than the x-ray sourcearray 2304, at least with respect to the direction of a tomosynthesisimaging arc to be subtended in the tomosynthesis imaging process.Preferably, the x-ray source array 2304 is large enough so as to be ableto subtend an appreciably large tomosynthesis imaging arc relative to apoint in the target volume. By way of example and not by way oflimitation, for the discussed IGRT implementation similar to that ofFIG. 4, supra, the x-ray source array 2304/406 should be at least about20 cm in length along the tomosynthesis imaging arc if separated fromthe treatment couch by 0.5 m-1.0 m, with better results being obtainedfor longer x-ray source array dimensions. Each x-ray source within thex-ray source array 2304 is collimated by the collimation device 2306such that the x-ray beam emanating therefrom is directed at the digitaldetector array 2302 and is only wide enough to cover the spatial extentof the digital detector array 2302. This is illustrated in FIG. 23B,which shows a collimated beam B1 emanating from an x-ray source S1 and acollimated beam B2 emanating from an x-ray source S2.

Inverse geometry configurations in the context of CT imaging arediscussed in U.S. Pat. No. 7,734,004B2 and US2006/021005A1, each ofwhich is incorporated by reference herein. Algorithms for tomosynthesisimaging based on inverse geometry configurations are also known in theart and, accordingly, implementation of the tomosynthesis imaging andreconstruction methods set forth herein would be achievable by a personskilled in the art in view of the present disclosure without undueexperimentation. Inverse geometry configurations can provide certainadvantages in tomographic imaging, with one important advantage beingreduced scatter in comparison to conventional configurations havinglarger detectors.

In accordance with one preferred embodiment, tomosynthesis imaging of atarget structure contained within a larger target volume is providedusing an inverse geometry tomosynthesis imaging system in a manner thatprovides at least one of increased image quality and reduced image dose,by virtue of actuating only a subset of the x-ray sources in the x-raysource array that are necessary to image the target structure in theinverse-geometry tomosynthesis imaging process based on a known orexpected location of the target structure. It has been foundparticularly useful to apply the method in the context of image-guidedradiation treatment systems, and still more particularly in theintrafraction tracking of a target structure, such as a tumor, that maybe moving during the treatment fraction. It is desirable to locate thetumor with a high degree of precision during the treatment fraction,while at the same time avoiding the excess introduction of ionizing kVimaging radiation into the target volume at locations away from thetumor location.

Referring now to FIGS. 23C-23D, it can be seen in FIG. 23C that thetarget structure T is in a first location and is encountered by thecollimated beams B1 from source S1 and B2 from source S2 on their way tothe digital detector array 2302, but is not encountered by thecollimated beams B3 from source S3 or B4 from source S4 on their way tothe digital detector array 2302. Accordingly, the tomosynthesisprojection images based on radiation from the sources S3 and S4 wouldnot be contributing any information relevant to the target structure Tin any tomosynthesis reconstructed data set. Likewise, it can be seen inFIG. 23D that the target structure T, which is now in a differentlocation within the target volume V, is encountered by the collimatedbeams B2 from source S2 and B3 from source S3, but is not encountered bythe collimated beams B1 from source S1 or B4 from source S4, and thusthe tomosynthesis projection images based on radiation from the sourcesS1 and S4 would not be contributing any relevant information in thetomosynthesis reconstructed data. According to a preferred embodiment,knowledge of the particular target structure location at any particulartime is used in the inverse geometry x-ray tomosynthesis imaging processto “turn off” any x-ray sources in the source array whose collimatedbeams do not pass through or near that structure (e.g., the subset 2310in FIG. 23C and the subset 2310′ in FIG. 23D), and to only activatethose x-ray sources whose collimated beams do pass through or near thatstructure (e.g., the subset 2308 in FIG. 23C and the subset 2308′ inFIG. 23D).

FIG. 24 illustrates inverse geometry tomosynthesis imaging of a targetstructure located within a target volume according to a preferredembodiment. At step 2402, information is received that is indicative ofan expected location of the target structure within the target volume ata first point in time, i.e., at the time at which the tomosynthesisimage volume will be acquired. This expected location information can bederived from a pilot tomosynthesis image data set acquired using all ofthe x-ray sources in the source array 2304, or alternatively from aprevious low-dose tomosynthesis imaging iteration. As anotheralternative, the expected location information can be derived from 2Dpilot x-ray images acquired using one of the x-ray sources, or from avery sparse set of tomosynthesis projection images acquired using only avery small subset (for example, every fifth x-ray source or every tenthx-ray source) of the x-ray sources. The use of a stereoscopicimplementation in which there are two separate inverse geometrytomosynthesis imaging systems can be especially helpful in providing alow-dose prediction of the target structure location from 2D pilot x-rayimages or sparse tomosynthesis projection image sets. Optionally,additional information from external sensing systems, such as theSYNCHRONY® respiratory tracking system, supra, can be incorporated intothe computation of the expected target structure location.

At step 2404, the expected location information is processed inconjunction with the known imaging geometry of the inverse geometrytomosynthesis imaging system to identify a first subset of the x-raysources whose collimated x-ray beams would pass through or near thetarget structure at the first point in time, as well as a second subsetof said x-ray sources whose collimated x-ray beams would not passthrough or near the target structure at the first point in time. At step2406, a first plurality of x-ray tomosynthesis projection images of thetarget structure is acquired during a first tomosynthesis imaginginterval that includes the first point in time, using only the firstsubset of x-ray sources and not the second subset of x-ray sources. Atstep 2408, in addition to using the acquired tomosynthesis image datafor its intended purpose, such as for reconstructing a tomosynthesisimage volume therefrom and guiding the delivery of treatment radiationto the target structure, the acquired tomosynthesis image data can befurther or otherwise processed to compute a next expected location ofthe target structure, which information can then be used again at step2404 for identifying the next subset of x-ray sources to use for thenext set of tomosynthesis projection images, and so on.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting.

What is claimed is:
 1. A method for tracking a target, the methodcomprising: receiving a planning image of a patient including thetarget, wherein the planning image has a first coordinate system;acquiring a diagnostic image of the patient in a second coordinatesystem, wherein said diagnostic image includes at least a portion of thetarget; acquiring a first tomosynthesis image of the patient in thesecond coordinate system, wherein the first tomosynthesis image isinherently registered with the diagnostic image, and wherein the firsttomosynthesis image includes at least a portion of the target;registering the diagnostic image with the planning image to obtain analignment transformation between the first coordinate system and thesecond coordinate system; acquiring a second tomosynthesis image of saidpatient, wherein said second tomosynthesis image includes at least aportion of the target; registering said second tomosynthesis image withsaid first tomosynthesis image to compute an intrafractiontransformation between the first coordinate system and the secondcoordinate system, wherein said intrafraction transformation determinesan approximate intrafraction location of the target in the secondcoordinate system relative to the first coordinate system; anddelivering treatment radiation to the target based at least in part onsaid intrafraction transformation and said alignment transformation. 2.The method of claim 1, wherein said intrafraction transformation, andwherein the first tomosynthesis image is acquired substantiallysimultaneously as acquisition of the diagnostic image.
 3. The method ofclaim 1, wherein said intrafraction transformation is characterized by anon-rigid transformation for accommodating elastic deformations in saidbody part during said treatment delivery.
 4. The method of claim 1,wherein a tomosynthesis imaging system used to acquire saidtomosynthesis images comprises at least one x-ray source in common witha two-dimensional stereotactic x-ray imaging system used to acquire saiddiagnostic images.
 5. The method of claim 1, wherein one or more offollowing applies: (i) a tomosynthesis imaging system used to acquiresaid tomosynthesis images comprises a digitally addressable x-ray sourcearray; (ii) said diagnostic image is a cone beam CT (CBCT) image andsaid first tomosynthesis image is obtained from a same data set used toform said CBCT image; (iii) the diagnostic image comprises a set ofstereo 2D x-ray images and said registering comprises (a) generating aplurality of digitally reconstructed radiograph (DRR) images from theplanning image and (b) registering the diagnostic images to the DRRimages to obtain the alignment transformation; (iv) the tomosynthesisimages are acquired using a stereoscopic x-ray imaging system includingdigitally addressable x-ray source arrays; (v) said diagnostic image isa cone beam CT (CBCT) image and said first tomosynthesis image isobtained from a same data set used to form said CBCT image acquiredusing digitally addressable x-ray source arrays; and (vi) the diagnosticimage comprises a set of stereo 2D x-ray images acquired using digitallyaddressable x-ray source arrays and said registering comprises (a)generating a plurality of digitally reconstructed radiograph (DRR)images from the planning image and (b) registering the diagnostic imagesto the DRR images to obtain the alignment transformation.
 6. A methodfor image guided radiation treatment of a body part, comprising:positioning the body part into a first treatment alignment relative toan image guided radiation treatment (IGRT) apparatus, said positioningincluding comparing (i) at least one two-dimensional stereotacticdigitally reconstructed radiograph (DRR) image derived from a referenceCT volume of the body part to (ii) at least one acquired two-dimensionalstereotactic x-ray image of the body part obtained during saidpositioning; acquiring a first tomosynthesis image data set of said bodypart with said body part substantially in said first treatmentalignment; acquiring at least one subsequent tomosynthesis data set ofsaid body part subsequent to said acquiring said first tomosynthesisimage data set; processing said at least one subsequent tomosynthesisimage data set in conjunction with said first tomosynthesis data set tocompute an in-treatment alignment variation of said body part; anddelivering treatment radiation to the body part based at least in parton said computed in-treatment alignment variation.
 7. A method for imageguided radiation treatment of a body part by an image-guided radiationtreatment (IGRT) apparatus, the IGRT apparatus including a treatmentguidance imaging system having a known geometry relative to a firstreference frame, the treatment guidance imaging system including atomosynthesis imaging system having a known geometry relative to saidfirst reference frame, the method comprising: receiving a pre-acquiredplanning image data set of the body part acquired in a second referenceframe generally independent of said first reference frame; acquiring aninitial diagnostic image data set of the body part in said firstreference frame using said treatment guidance imaging system; computinga first registration between said initial diagnostic image data set andsaid planning image data set; acquiring an initial tomosynthesis imagedata set of said body part in said first reference frame using saidtomosynthesis imaging system, said initial tomosynthesis image data sethaving an inherent registration with said initial diagnostic image dataset; acquiring a subsequent tomosynthesis image data set in said firstreference frame using said tomosynthesis imaging system at a timesubsequent to said initial tomosynthesis image data set acquisition;computing a second registration between said subsequent tomosynthesisimage data set and said initial tomosynthesis image data set; anddelivering treatment radiation to the body part based at least in parton information derived from (i) said first registration, (ii) saidinherent registration, and (iii) said second registration.
 8. The methodof claim 7, further comprising: acquiring a time sequence of saidsubsequent tomosynthesis image data sets on a continuing basisthroughout a radiation treatment fraction; for each member of said timesequence of subsequent tomosynthesis image data sets, computing saidsecond registration between that member and said initial tomosynthesisimage data set; and adapting, on a continuing basis throughout aradiation treatment fraction, said delivery of treatment radiation tothe body part based on a most recent one of said second registrations.9. The method of claim 7, wherein said diagnostic image data set is twodimensional projection x-ray data, said planning image data set is aplanning CT image data set, and said computing the first registrationbetween said initial diagnostic image data set and said planning imagedata set comprises: generating a set of digitally reconstructedradiographs (DRRs) from said planning CT image data set, wherein saidset of DRRs is generated from the perspective of the first referenceframe; registering said two dimensional projection x-ray data with saidset of DRRs; determining which of said set of DRRs best matches said twodimensional projection x-ray data to obtain an alignment transformationbetween the first coordinate system and the second coordinate system.10. The method of claim 9, wherein said two dimensional projection x-raydata comprises a pair of stereoscopic two dimensional projection x-raydata.
 11. The method of claim 9, wherein said two dimensional projectionx-ray data comprises monoscopic two dimensional projection x-ray data.12. The method of claim 7, wherein said diagnostic image data set is asetup cone beam CT (CBCT) image data set, said planning image data setis a planning CT image data set, and said computing the firstregistration between said initial diagnostic image data set and saidplanning image data set comprises: performing a 3D-3D registrationbetween said setup CBCT image data set and said planning CT image dataset.
 13. The method of claim 12, wherein data for said initialtomosynthesis data set is acquired from said setup CBCT data set. 14.The method of claim 9, wherein at least one of said first coordinatetransformation and said first alignment variation is characterized by anon-rigid transformation.
 15. The method of claim 7, wherein saidinitial tomosynthesis image data set is acquired substantiallysimultaneously with said initial diagnostic image data set, and whereinsaid inherent registration between said initial tomosynthesis image dataset and said initial medical image data set is characterized by one ormore predetermined coordinate transformations that are fixed accordingto a fixed imaging geometry of the treatment guidance imaging systemincluding said tomosynthesis imaging system relative to said IGRTapparatus.
 16. The method of claim 7, wherein said computing the secondregistration between said initial tomosynthesis image data set and saidsubsequent tomosynthesis image data set comprises a direct computationof anatomical and/or positional variations of the body part between saidinitial and subsequent tomosynthesis imaging times relative to areference frame of the tomosynthesis imaging system, whereby saidcomputing the second registration does not require computationsassociated with imaging geometry and/or reference frame differences,thereby promoting at least one of reduced intra-fraction computationalintensity and reduced treatment radiation delivery margins.
 17. Themethod of claim 7, wherein the pre-acquired image data set comprises athree-dimensional (3D) image volume, wherein said treatment guidanceimaging system comprises a two-dimensional (2D) stereotactic x-rayimaging system, and wherein the method further comprises: computing apopulation of 2D stereotactic digitally reconstructed radiograph (DRR)images based on the pre-acquired 3D image volume and the imaginggeometry of the treatment guidance imaging system; and positioning thebody part into said initial treatment position, said positioningincluding comparing said 2D DRR images with a plurality of 2Dstereotactic x-ray images acquired using said 2D stereotactic x-rayimaging system; wherein said initial medical image data set comprises aone of said 2D stereotactic x-ray images acquired with said body part insaid initial treatment position.
 18. The method of claim 17, whereinsaid pre-acquired 3D image volume is a CT image volume.
 19. The methodof claim 17, wherein said pre-acquired 3D image volume is a cone beam CT(CBCT) image volume.
 20. The method of claim 17, wherein said 2Dstereotactic x-ray imaging system has at least one of an x-ray sourceand an x-ray detector in common with said tomosynthesis imaging system.21. The method of claim 7, wherein the pre-acquired image data setcomprises a three-dimensional (3D) image volume, wherein said treatmentguidance imaging system comprises a cone beam CT (CBCT) imaging system,and wherein the method further comprises: positioning the body part intosaid initial treatment position, said positioning including comparingsaid 3D image volume with a plurality of CBCT image volumes acquiredusing said CBCT imaging system; wherein said initial medical image dataset comprises a one of said CBCT image volumes acquired with said bodypart in said initial treatment position.
 22. The method of claim 21,wherein said pre-acquired 3D image volume is a CT image volume.
 23. Themethod of claim 21, wherein said pre-acquired 3D image volume is a conebeam CT (CBCT) image volume.
 24. The method of claim 21, wherein saidcomparing said 3D image volume with said plurality of CBCT image volumescomprises: computing a population of digitally reconstructedtomosynthesis (DRT) image data sets based on the pre-acquired 3D imagevolume and the imaging geometry of the CBCT imaging system; andpositioning the body part into said initial treatment position, saidpositioning including comparing a one of said DRT image data sets with aone of said CBCT image volumes.
 25. The method of claim 24, wherein saidcomparing the DRT image data set with CBCT image volume comprises:processing the DRT image data set to compute a 3D DRT image volume; andperforming a 3D-3D comparison between the 3D DRT image volume and theCBCT image volume.
 26. The method of claim 24, wherein said comparingthe DRT image data set with the CBCT image volume comprises performing acomparison between said DRT image data set and an auxiliary setuptomosynthesis data set, wherein said auxiliary setup tomosynthesis dataset comprises at least one of (i) an auxiliary setup DRT data setcomputed from said CBCT image volume based on the imaging geometry ofthe CBCT imaging system, and (ii) a subset of CBCT projection imagesused to generate the CBCT image volume, the subset corresponding to animaging arc that is less than 180 degrees.
 27. The method of claim 26,wherein said performing the comparison between said DRT image data setand the auxiliary setup tomosynthesis data set comprises: processing theDRT image data sets to compute a 3D DRT image volume; processing theauxiliary setup tomosynthesis data set to compute an auxiliary setuptomosynthesis image volume; and performing a 3D-3D registration betweensaid 3D DRT image volume and said auxiliary setup tomosynthesis imagevolume.
 28. The method of claim 27, wherein said performing the 3D-3Dregistration comprises: identifying a first image slice within said 3DDRT image volume for which an anatomical object of interest is in focus;identifying a second image slice within said setup tomosynthesis imagevolume for which the anatomical object of interest is in focus; andperforming a 2D-2D registration between said first and second imageslices.
 29. The method of claim 21, wherein said tomosynthesis imagingsystem has at least one of an x-ray source and an x-ray detector incommon with said CBCT imaging system.
 30. The method of claim 29,wherein said tomosynthesis imaging system is integral with said CBCTimaging system.
 31. The method of claim 7, wherein said pre-acquiredimage data set is acquired by a reference imaging system selected fromthe group consisting of: conventional CT imaging systems; cone-beam CT(CBCT) imaging systems; magnetic resonance imaging (MRI) systems;ultrasound imaging systems; and tomosynthesis imaging systems.
 32. Themethod of claim 7, wherein said initial medical image data set of thebody part is acquired by a medical imaging system that is a component ofthe treatment guidance imaging system and selected from the groupconsisting of: two-dimensional (2D) stereotactic x-ray imaging systems;cone-beam CT (CBCT) imaging systems; and ultrasound imaging systems. 33.The method of claim 7, wherein said tomosynthesis imaging systemcomprises at least one x-ray source selected from the group consistingof: x-ray point sources; and digitally addressable x-ray source arrays.34. The method of claim 33, wherein said tomosynthesis imaging system isselected from the group consisting of: single-arc x-ray tomosynthesissystems; stereo x-ray tomosynthesis systems; and multiple-arc x-raytomosynthesis systems.
 35. The method of claim 34, wherein saidtomosynthesis imaging system is selected from the group consisting of:single-energy x-ray tomosynthesis systems; dual-energy x-raytomosynthesis systems; and multiple-energy x-ray tomosynthesis systems.36. The method of claim 7, wherein said initial diagnostic image dataset is the same as said initial tomosynthesis image data set, saidpre-acquired planning image a planning CT image data set, and computingsaid first registration comprises registration of said initialtomosynthesis image data set with said CT planning image data set.
 37. Amethod for image guided radiation treatment of a body part by animage-guided radiation treatment (IGRT) apparatus, the IGRT apparatusincluding a tomosynthesis imaging system having a known geometryrelative to a reference frame of the IGRT apparatus, the methodcomprising: receiving a pre-acquired image data set of the body partacquired in a reference frame generally independent of the referenceframe of the IGRT apparatus; acquiring an initial tomosynthesis imagedata set of the body part using said tomosynthesis imaging system whilesaid body part is in an initial treatment position relative to the(IGRT) apparatus; computing a first registration between said initialtomosynthesis image data set and said pre-acquired image data set;acquiring a subsequent tomosynthesis image data set using saidtomosynthesis imaging system at a time subsequent to said initialtomosynthesis image data set acquisition; computing a secondregistration between said subsequent tomosynthesis image data set andsaid initial tomosynthesis image data set; and delivering treatmentradiation to the body part based at least in part on information derivedfrom (i) said first registration between said initial tomosynthesisimage data set and said pre-acquired image data set and (ii) said secondregistration between said subsequent tomosynthesis image data set andsaid initial tomosynthesis image data set.
 38. The method of claim 37,wherein said delivering treatment radiation to the body part comprises:computing a third registration between said subsequent tomosynthesisimage data set and said pre-acquired image data set based on a serialapplication of said second registration and said first registration; andapplying treatment radiation to the body part based at least in part onsaid third registration as applied to a radiation treatment deliveryplan developed using said pre-acquired image data set.
 39. The method ofclaim 37, further comprising: acquiring a time sequence of saidsubsequent tomosynthesis image data sets on a continuing basisthroughout a radiation treatment fraction; for each member of said timesequence of subsequent tomosynthesis image data sets, computing saidsecond registration between that member and said initial tomosynthesisimage data set; and adapting, on a continuing basis throughout aradiation treatment fraction, said delivery of treatment radiation tothe body part based on a most recent one of said second registrations.40. The method of claim 39, wherein said adapting said delivery oftreatment radiation to the body part comprises: computing a thirdregistration between said most recent subsequent tomosynthesis imagedata set and said pre-acquired image data set based on a serialapplication of said second registration said first registration; andapplying treatment radiation to the body part based at least in part onsaid third registration as applied to a radiation treatment deliveryplan developed using said pre-acquired image data set; wherein saidfirst registration remains fixed throughout said radiation treatmentfraction; whereby registrations between image data sets corresponding todifferent frames of reference do not require repeated computationthroughout the radiation treatment fraction, thereby promoting at leastone of reduced intra-fraction computational intensity and reducedtreatment radiation delivery margin.
 41. The method of claim 37, whereinsaid computing the first registration between said initial tomosynthesisimage data set and said pre-acquired image data set comprises: computinga first coordinate transformation associated with imaging geometryand/or reference frame differences between a reference imaging systemused to acquire said pre-acquired image data set and said tomosynthesisimaging system of said IGRT apparatus; and computing a first alignmentvariation associated with underlying anatomical and/or positionalvariations of the body part between said acquisitions by said referenceimaging system and said tomosynthesis imaging system.
 42. The method ofclaim 41, wherein at least one of said first coordinate transformationand said first alignment variation is characterized by a non-rigidtransformation.
 43. The method of claim 37, wherein said computing thesecond registration between said initial tomosynthesis image data setand said subsequent tomosynthesis image data set comprises a directcomputation of anatomical and/or positional variations of the body partbetween said initial and subsequent tomosynthesis imaging times relativeto a reference frame of the tomosynthesis imaging system, whereby saidcomputing the second registration does not require computationsassociated with imaging geometry and/or reference frame differences,thereby promoting at least one of reduced intra-fraction computationalintensity and reduced treatment radiation delivery margins.
 44. Themethod of claim 37, the pre-acquired image data set comprising athree-dimensional (3D) image volume, the method further comprising:computing a population of digitally reconstructed tomosynthesis (DRT)image data sets based on the pre-acquired 3D image volume and theimaging geometry of the tomosynthesis imaging system; and positioningthe body part into said initial treatment position, said positioningincluding comparing said DRT image data sets with a plurality of setuptomosynthesis image data sets acquired using said tomosynthesis imagingsystem; wherein said initial tomosynthesis image data set comprises aone of said setup tomosynthesis image data sets acquired with said bodypart in said initial treatment position.
 45. The method of claim 44,wherein said pre-acquired 3D image volume is a CT image volume.
 46. Themethod of claim 44, wherein said pre-acquired 3D image volume is a conebeam CT (CBCT) image volume.
 47. The method of claim 44, wherein saidcomparing said DRT image data sets with said setup tomosynthesis imagedata sets comprises: processing a one of said DRT image data sets togenerate therefrom a 3D DRT image volume; processing a one of said setuptomosynthesis image data sets to generate therefrom a 3D setuptomosynthesis image volume; and performing a 3D-3D registration betweensaid 3D DRT image volume and said 3D setup tomosynthesis image volume.48. The method of claim 44, wherein said performing the 3D-3Dregistration comprises: identifying a first image slice within said 3DDRT image volume for which an anatomical object of interest is in focus;identifying a second image slice within said 3D setup tomosynthesisimage volume for which the anatomical object of interest is in focus;and performing a 2D-2D registration between said first and second imageslices.
 49. The method of claim 37, wherein each of said initialtomosynthesis image data set and said subsequent tomosynthesis imagedata set is a stereoscopic tomosynthesis data set including a firstchannel tomosynthesis image data set acquired over a first acquisitionarc and a second channel tomosynthesis image data set acquired over asecond acquisition arc non-overlapping with said first acquisition arc.50. The method of claim 49, wherein said computing the firstregistration between said initial tomosynthesis image data set and saidpre-acquired image data set comprises: combining information from saidfirst and second channel tomosynthesis data sets of said initialtomosynthesis image data set to generate a resultant initial imagevolume; and registering said resultant initial image volume to saidpre-acquired image data set.
 51. The method of claim 49, wherein saidcomputing the first registration between said initial tomosynthesisimage data set and said pre-acquired image data set comprises:separately registering each of said first and second channeltomosynthesis data sets of said initial tomosynthesis image data set tosaid pre-acquired image data set; and combining information from saidseparate registrations to compute said first registration.
 52. Themethod of claim 49, wherein said tomosynthesis imaging system comprisesfirst and second x-ray source arrays corresponding respectively to saidfirst and second channel tomosynthesis data sets.
 53. The method ofclaim 52, wherein said first and second x-ray source arrays arenon-moving relative to the reference frame of the IGRT apparatus. 54.The method of claim 37, wherein each of said initial tomosynthesis imagedata set and said subsequent tomosynthesis image data set is adual-energy tomosynthesis data set.
 55. The method of claim 54, whereineach of said initial tomosynthesis image data set and said subsequenttomosynthesis image data set is a stereoscopic tomosynthesis data setincluding a first channel tomosynthesis data set acquired over a firstacquisition arc and a second channel tomosynthesis image data setacquired over a second acquisition arc non-overlapping with said firstacquisition arc.
 56. The method of claim 55, each of said first channeltomosynthesis data sets corresponding to a first x-ray energy and eachof said second channel tomosynthesis data sets corresponding to a secondx-ray energy different than said first x-ray energy.
 57. The method ofclaim 37, the pre-acquired image data set comprising a three-dimensional(3D) image volume, the method further comprising positioning the bodypart into said initial treatment position, said positioning includingcomparing said pre-acquired 3D image volume with a plurality of setuptomosynthesis image data sets acquired using said tomosynthesis imagingsystem, wherein said initial tomosynthesis image data set comprises aone of said setup tomosynthesis image data sets acquired with said bodypart in said initial treatment position.
 58. The method of claim 57,wherein said pre-acquired 3D image volume is a CT image volume.
 59. Themethod of claim 58, wherein said pre-acquired 3D image volume is a conebeam CT (CBCT) image volume.
 60. The method of claim 57, wherein saidcomparing said pre-acquired 3D image volume with said setuptomosynthesis image data sets comprises: processing a one of said setuptomosynthesis image data sets to generate therefrom a 3D setuptomosynthesis image volume; and performing a 3D-3D registration betweensaid pre-acquired 3D image volume and said 3D setup tomosynthesis imagevolume.
 61. The method of claim 57, wherein each of said setuptomosynthesis image data sets is a stereoscopic tomosynthesis data set.62. The method of claim 57, wherein each of said setup tomosynthesisimage data sets is a dual-energy tomosynthesis data set.
 63. Animage-guided radiation treatment (IGRT) system, having a first referenceframe, comprising: a tomosynthesis imaging system having a knowngeometry relative to the first reference frame, the tomosynthesisimaging system to: acquire an initial tomosynthesis image data set of abody part while said body part is in an initial treatment positionrelative to the IGRT system; and acquire a subsequent tomosynthesisimage data set at a time subsequent to said initial tomosynthesis imagedata set acquisition; a system controller to: receive a pre-acquiredimage data set of the body part acquired in a second reference framegenerally independent of the first reference frame; compute a firstregistration between said initial tomosynthesis image data set and saidpre-acquired image data set; and compute a second registration betweensaid subsequent tomosynthesis image data set and said initialtomosynthesis image data set; and a radiation treatment source todeliver treatment radiation to the body part based at least in part oninformation derived from (i) said first registration between saidinitial tomosynthesis image data set and said pre-acquired image dataset and (ii) said second registration between said subsequenttomosynthesis image data set and said initial tomosynthesis image dataset.
 64. The system of claim 63, wherein: the system controller is tocompute a third registration between said subsequent tomosynthesis imagedata set and said pre-acquired image data set based on a serialapplication of said second registration and said first registration; andthe radiation treatment source is to apply treatment radiation to thebody part based at least in part on said third registration as appliedto a radiation treatment delivery plan developed using said pre-acquiredimage data set.
 65. The system of claim 63, wherein: the tomosynthesisimaging system is to acquire a time sequence of a plurality ofsubsequent tomosynthesis image data sets on a continuing basisthroughout a radiation treatment fraction, the subsequent tomosynthesisimage data set being a member of the plurality of subsequenttomosynthesis image data sets; for each member of said plurality ofsubsequent tomosynthesis image data sets, the system controller is tocompute said second registration between that member and said initialtomosynthesis image data set; and the radiation treatment source is toadapt, on a continuing basis throughout a radiation treatment fraction,said delivery of treatment radiation to the body part based on a mostrecent one of said second registrations.
 66. The system of claim 63,wherein said computing the first registration between said initialtomosynthesis image data set and said pre-acquired image data setcomprises: computing a first coordinate transformation associated withimaging geometry and/or reference frame differences between a referenceimaging system used to acquire said pre-acquired image data set and saidtomosynthesis imaging system; and computing a first alignment variationassociated with underlying anatomical and/or positional variations ofthe body part between said acquisitions by said reference imaging systemand said tomosynthesis imaging system.
 67. The system of claim 66,wherein at least one of said first coordinate transformation and saidfirst alignment variation is characterized by a non-rigidtransformation.
 68. The system of claim 63, wherein said computing thesecond registration between said initial tomosynthesis image data setand said subsequent tomosynthesis image data set comprises a directcomputation of anatomical and/or positional variations of the body partbetween said initial tomosynthesis image data set and said subsequenttomosynthesis image data set, wherein said computing the secondregistration does not require computations associated with imaginggeometry and/or reference frame differences, thereby promoting at leastone of reduced intra-fraction computational intensity and reducedtreatment radiation delivery margins.
 69. The system of claim 63, thepre-acquired image data set comprising a three-dimensional (3D) imagevolume, wherein the system controller is further to: compute a pluralityof digitally reconstructed tomosynthesis (DRT) image data sets based onthe pre-acquired 3D image volume and imaging geometry of thetomosynthesis imaging system; and position the body part into saidinitial treatment position, said positioning comprising comparing saidplurality of DRT image data sets with a plurality of setup tomosynthesisimage data sets acquired using said tomosynthesis imaging system;wherein said initial tomosynthesis image data set comprises one of saidplurality of setup tomosynthesis image data sets.
 70. The system ofclaim 63, wherein each of said initial tomosynthesis image data set andsaid subsequent tomosynthesis image data set is a stereoscopictomosynthesis data set comprising a first channel tomosynthesis imagedata set acquired over a first acquisition arc and a second channeltomosynthesis image data set acquired over a second acquisition arcnon-overlapping with said first acquisition arc.
 71. A systemcomprising: a diagnostic imaging system to acquire a diagnostic image ofa patient in a first coordinate system, wherein said diagnostic imagecomprises at least a portion of a target; a tomosysnthesis imagingsystem to: acquire a first tomosynthesis image of the patient in thefirst coordinate system, wherein the first tomosynthesis image isinherently registered with the diagnostic image, and wherein the firsttomosynthesis image comprises at least a portion of the target; andacquire a second tomosynthesis image of said patient, wherein saidsecond tomosynthesis image comprises at least a portion of the target;and a system controller to: receive a planning image of the patientincluding the target, wherein the planning image has a second coordinatesystem; register the diagnostic image with the planning image to obtainan alignment transformation between the second coordinate system and thefirst coordinate system; and register said second tomosynthesis imagewith said first tomosynthesis image to compute an intrafractiontransformation between the second coordinate system and the firstcoordinate system, wherein said intrafraction transformation determinesan approximate intrafraction location of the target in the firstcoordinate system relative to the second coordinate system.
 72. Thesystem of claim 71, further comprising: a treatment radiation source todeliver treatment radiation to the target based at least in part on saidintrafraction transformation and said alignment transformation.
 73. Thesystem of claim 71, wherein said intrafraction transformation ischaracterized by a rigid body transformation, and wherein the firsttomosynthesis image is acquired substantially simultaneously asacquisition of the diagnostic image.
 74. The system of claim 71, whereinsaid intrafraction transformation is characterized by a non-rigidtransformation for accommodating elastic deformations in said body part.75. The system of claim 71, wherein the diagnostic imaging systemcomprises a two-dimensional stereotactic x-ray imaging system andwherein the tomosynthesis imaging system comprises at least one x-raysource in common with the diagnostic imaging system.